The Duration of the Sun.

THERMOSCOPIC BALANCE.

TheBuilders' Weekly Reporter(London) has an interesting account of a lecture at the Royal Institute, given by Professor Sir William Thomson, on the latest dynamical theories regarding the "probable origin, total amount, and possible duration of the sun's heat." During the short 3,000 years or more of which man possesses historic records there was, the learned physicist showed, no trace of variation in solar energy; and there was no distinct evidence of it even though the earth, as a whole, from being nearer the sun, received in January 6½ per cent more heat than in July. But in the millions of years which geology carried us back, it might safely be said there must have been great changes. How had the solar fires been maintained during those ages? The scientific answer to this question was the theory of Helmholtz that the sun was a vast globe gradually cooling, but as it cooled, shrinking, and that the shrinkage—which was the effect of gravity upon its mass—kept up its temperature. The total of the sun's heat was equal to that which would be required to keep up 476,000 millions of millions of millions horse power, or about 78,000 horse power for every square meter—a little more than a square yard—and yet the modern dynamical theory of heat shows that the sun's mass would require only to fall in or contract thirty-five meters per annum to keep up that tremendous energy. At this rate, the solar radius in 2,000 years' time would be about one hundredth per cent less than at present. A time would come when the temperature would fall, and it was thus inconceivable that the sun would continue to emit heat sufficient to sustain existing life on the globe for more than 10,000,000 years. Applying the same principles retrospectively, they could not suppose that the sun had existed for more than twenty million years, no matter what might have been its origin—whether it came into existence from the clash of worlds pre-existing, or of diffused nebulous matter. There was a great clinging by geologists and biologists to vastly longer periods, but the physicist, treating it as a dynamic question with calculable elements, could come to no other conclusion materially different from what he had stated. Sir William Thomson declined to discuss any chemical source of heat, which, whatever its effect when primeval elements first came into contact, was absolutely insignificant compared with the effects of gravity after globes like the sun and the earth had been formed. In all these speculations they were in the end driven to the ultimate elements of matter, to the question—when they thought what became of all the sun's heat—what is the luminiferous ether that fills space, and to that most wonderful form of force upon which Faraday spent so much of the thought of his later years—gravity. The lecture was heard with deep interest and close attention.

The twin screw dredger Dolphin was recently constructed for the Colonies, under the direction of Sir John Coode, assisted by Mr. Wm. Matthews, C.E., and is especially designed, says theEngineer, for harbor improvements in the West Indies. The dimensions are:

The boiler is of steel, for a working pressure of 90 lb. per square inch. The bucket ladder works through a well formed in the center of the vessel, and dredges to a depth of 33 ft. below the water level, and the buckets are made wholly of steel, and are capable of lifting 250 tons of free soil per hour. Triple-geared winches are supplied at bow and stern for working the mooring chains, the barrels of which can be worked independently or conjointly, as required. The cabins for the officers and crew are of the most complete description; those of the former being fitted on starboard side of the well, and consist of rooms for the captain, mate, and engineers, also mess room. All the rooms are large and efficiently lighted and ventilated. A powerful crane is erected at forward end for overhauling the buckets, hoisting gear, etc.

THE DREDGER DOLPHIN.

At a recent meeting of the Engineers' Club of Philadelphia, a paper by Conway B. Hunt was read on hydraulic dredging machinery.

The paper mentions the early application of the principle of hydraulic dredging, that is, the mixing of dredged material with water and then removing the mixture by suction or otherwise; and after referring briefly to the Roy Stone and Bowers dredges as typical machines, describes in detail the Von Schmidt dredge. Two of these dredges are engaged on the improvement of the Potomac River at Washington, D. C., under the United States Government. Each is 100 feet by 50 feet, with a semicircular bow, around which travels a vertical suction pipe, 22 in. in diameter, and telescopic. At its foot is a conical hood, beneath which works a rotary excavating plow, 8 feet in diameter. The suction is produced by a powerful centrifugal pump, run by a 200 horse power engine.

The discharge pipe is 20 in. in diameter, has rubber hose joint connections, and is carried to the shore on pontoons. The material was mixed with from three to ten times its volume of water, and discharged at distances up to 3,500 feet from the dredge, and at from 6 to 10 feet above water. A year's record shows an average of 175 cubic yards per working hour, and 2,300 yards per day, for each dredge. The work was done, by contract, at prices of 12.37 cts., 15 cts., and 15.45 cts. per cubic yard, which includes the cost of levees to confine the semi fluid material, drains to carry off the water, etc. The final estimates were specified to be taken by cross sections of the completed fill after it had become solidified and compacted. In conclusion, it is noted that the devices and details of hydraulic dredging machines are the subjects of numerous patents, and their most efficient combination may be long deferred. The large number of machines that are still in the experimental stage of development would indicate that the best results attainable from this class of dredges have not yet been accomplished.

The details of the process vary with quality of beets. To a vat containing the secondary products to be treated are added calculated quantities of diluted hydrochloric acid and milk of lime at 25° B. The mass is heated to the boiling point by a steam coil. In a separate vat the product is diluted with water at 75° C. to 23° B., and subsequently run through Puvrez filtering bags. The filtrate is clear in color, and is received in a measuring tank, from which it is run into the diffusion battery. In the latter but few changes are necessary. It is said that by this method an additional 1 per cent sugar is extracted from the beet, and the white sugar obtained can be at once placed upon the market.

Therewere exported last season from Prince Edward Island 91,000 cases of lobsters.

When, in 1752, Franklin succeeded, through a kite sent up into a storm cloud, in obtaining an electric spark at the extremity of the cord, which had been made a conductor through the rain, it was no longer possible to doubt that lightning was but an immense electric discharge between two clouds, or a discharge between a cloud and the earth. This discovery was of great importance, since it connected with the laws of physics certain phenomena which, until then, had passed for marvelous, and in which nothing but supernatural and mysterious manifestations were seen.

The aurora borealis, which is more difficult to understand, and which necessitates more extended scientific notions, has remained much longer unexplained. This enigmatic phenomenon was especially striking to the imagination of ancient peoples. It was regarded as an omen of inauspicious events, and the historians who describe it affirm that, at times, armies have been seen passing through the bloody heavens, and that the clash of arms has been heard.

It is now known that the aurora borealis has the same origin as lightning, that it is one of the visible manifestations of atmospheric electricity, and that it is due to slow movements of that fluid, while lightning is the result of violent motions. The effects of the aurora and of the thunderbolt are absolutely different; but between them there is an intermediary that connects them, and this is heat lightning.

These elementary notions are now the property of science; but the study of the aurora has hitherto been only partially outlined. Travelers and physicists have, indeed, given numerous descriptions, but it has remained to find the bonds that unite these so important phenomena in the economy of the globe, to study the causes that set them in action, to observe the correlations that they may offer, and to discuss theories. This is a labor that Mr. S. Lemstrom has been engaged in for several years, and we now propose to analyze the results published by this great Finnish physicist.

The author of this important work, who has long been occupied in the study of the aurora borealis, so frequent in his country, was attached to the polar expedition made in 1868 by Nordenskjold. He was led to begin a series of important observations. In 1871 he visited Finnish Lapland, and, after a series of ingenious researches, constructed an apparatus that permitted him to artificially reproduce the light of the aurora, and to present science with a summary of new and incontestable facts.

Mr. Lemstrom has observed a large number of auroræ, and before touching upon theoretic questions, we shall give his description of one of the phenomena that seems to him to be the completest. On the 18th of October, 1868, the steamer Sophia was nearing the coast of Norway, after battling with a furious sea for three days in succession.

"To the west of the horizon we remarked two strata of clouds that were clearly separated by a blue band of the heavens, crossed by a band striated with a pale yellow. It was the feeble beginning of an aurora, whose splendor was soon to surpass all the phenomena of the same kind that we had up till then observed. The edges of the upper stratum of clouds gradually lighted up, and we soon saw isolated flames issuing from them that sometimes rose to the zenith. Suddenly, the phenomenon embraced the entire horizon. Everywhere were flames, everywhere were jets of brilliant light, yellow below, green in the center, and reddish violet above. In an instant, all the rays united in a regular and dazzling crown, situated in the heavens to the south of the zenith. When the phenomenon reached the maximum of its intensity, it reminded us of the immense vault of a temple, with a brilliant chandelier in the center. The apparition lasted but a few minutes, but, on vanishing, left behind it a luminous zone between the banks of clouds. From the upper bank there continued to emanate, at short intervals, isolated rays that rose to the zenith, and there formed the fragments of a crown. The edges of the banks of clouds remained luminous, although the rays had disappeared."

Fig. 4.—AURORAL LIGHT AROUND THE SUMMIT OF A MOUNTAIN.Fig. 2.—AURORA BOREALIS OBSERVED IN LAPLAND.Fig. 3.—AURORA BOREALIS OBSERVED AT THE PRESBYTERY OF ENARE.

Fig. 4.—AURORAL LIGHT AROUND THE SUMMIT OF A MOUNTAIN.

Fig. 2.—AURORA BOREALIS OBSERVED IN LAPLAND.

Fig. 3.—AURORA BOREALIS OBSERVED AT THE PRESBYTERY OF ENARE.

Fig. 1.—AURORA BOREALIS OBSERVED NEAR THE COAST OF NORWAY.

According to Mr. Lemstrom, Fig. 1 gives an idea, although a feeble one, of the phenomenon at its height. It reproduces only half of the horizon, and the reader may supply the missing portion of this grand spectacle in imagination. The streams of light verging toward a common center were alternately rose colored and pale yellow, and overlooked an immense violet zone. The rosette in the center was of a beautiful red, and stood out upon a greenish blue circle.

Fig. 2 represents an aurora that was observed on the 19th of November, 1871, in Finnish Lapland. At the beginning, and at 30° above the horizon, it formed an arch from whence rose waves of light, and which gradually ascended. The figure shows it when it had reached about 60° above the horizon. The base of the aurora was yellow, and the oblique and very brilliant rays were, slightly higher up, rosy, violet, and blue. The colors of the polar light are usually clear and bright, but never did they exhibit greater luster than on this occasion.

Fig. 3 gives an idea of the variety of forms that the phenomenon may affect. It represents an aurora that was observed at the presbytery of Enare on the 16th of November, 1871. The aurora this time took on the form of a glowing red band, curved as shown in the figure. The two extremities bordered on yellow and green.

There is another form of aurora frequently observed in northern countries, and that is the one that is seen to occur above clouds, and that has the appearance of a wide piece of drapery with undulating folds. As it is the form most usually represented, we shall not dwell upon it. On the contrary, we shall speak of other phenomena of the same origin, and much less known, that Mr. Lemstrom describes. It concerns those auroral lights that shine at the edges of clouds, or that form around the tops of the mountains in Spitzbergen or in the Alpine districts of Lapland. According to the Finnish observer, it would be impossible to tell by the naked eye whence this light comes, but, by means of a spectroscope, we find that it is of the same nature as the aurora. Sometimes, these strange lights take on the form of flames of but little brightness, which, at short intervals, rise from the crest of the mountain and suddenly vanish (Fig. 4).

These phenomena sometimes exhibit themselves at the level of the earth's surface, or upon the roofs of houses.

Finally, Mr. Lemstrom describes the diffuse light which sometimes fills the atmosphere of the polar regions, thus proving that the phenomenon shows itself from time to time in the vicinity of the earth itself.

Meteors of the same nature as the light of the auroræ boreales do not occur solely in the polar regions, and the author demonstrates, not without attaching much importance to it from the standpoint of the theories to which he has been led, that they are observed in other countries of the earth. In Peru, Bolivia, and Chili the summits of the mountains are often seen illuminated by a brilliant light. This light, which occurs especially in summer, has been compared to heat lightning by scientists.

Similar observations have been made in the Swiss Alps. Dr. De Saussure has seen electricity escape through all the projecting parts of objects, and the same phenomena have been observed upon the high plateaus of Mexico. Again, we may cite the fact that Brewster observed a light upon a church tower during an aurora borealis. In every country phenomena similar to polarized light may occur.—La Nature.

In1886, 17 Gloucester fishing vessels were lost, worth $115,800, and 115 fishermen never came home. The year was remarkable for the small inshore catch, almost all the fishing being done on the high seas.

At the forthcoming American Exhibition in London, we are promised, among other novelties, a house of straw, which is now being made in Philadelphia. This house is to represent an American suburban villa, announced to be "handsome and artistic in design," two and a half stories high, and covering a space of 42 feet by 50 feet. It is constructed entirely of materials manufactured from straw—foundations, timbers, flooring, sheathing, roofing, everything in fact, including the chimneys—the material being fire proof as well as water proof. The inside finish is to be in imitation rosewood, mahogany, walnut, maple, ash, ebony, and other fine woods, the straw lumber taking perfectly the surface and color of any desired wood. This straw house is, in the first place, to illustrate Philadelphia's commercial, financial, and industrial interests by means of large photographs of the leading buildings; but it will also demonstrate how far the inventive Yankee has succeeded, not in showing us how to make bricks without straw, but how to produce timber from straw. If, after this brilliant exhibition of inventive genius, we do not bow down and worship him as the "licker" of creation, we may consider ourselves lost to all sense of what is proper under the circumstances.—Iron.

The British government lately strengthened up the bottom of the old ironclad Resistance, and tried the effect of firing off a 90 lb. guncotton torpedo against the vessel. To the surprise of every one, the ship was not seriously damaged. TheEngineercomments upon the experiment as follows:

The Resistance experiments so far tend to demonstrate that the total disablement or destruction of a modern ironclad is not so easy as many people imagined. It was too hastily assumed that the explosion of a charge of 90 lb. of guncotton in contact with any portion of the hull under water would have such destructive effect as to overcome the protection afforded by a thick lining of coal and the cellular system of construction now always adopted in vessels of war. There are, however, certain considerations attached to this experiment which, if duly weighed, should reassure the advocates of the torpedo, and restrain the exultation of naval architects within reasonable bounds. We shall endeavor to place these before our readers briefly and impartially, reserving a fuller summing-up until the remaining experiments are concluded, as they are of greater importance than any of those preceding. It is the more essential to do this because theTimes, in a leading article of November 3, leads us to believe that as this attack failed, in the broad sense of the word, similar attempts under different conditions would have a like result: and that although serious damage would be caused, the ship would remain "floating and seaworthy, with her offensive powers not materially impaired." We are not prepared to accept this conclusion, for the following reasons:

First, let us consider the general effect of a submarine explosion. It closely resembles the action of gunpowder when ignited in a gun. We know that in the latter case a quantity of heated gas is formed, which in its power of expansion exerts force in all directions. Prevented from expanding by its rigid confinement, except in the direction of the bore, the gas attains its object by the displacement of the projectile. This is, in fact, the line of least resistance. When the same explosive is ignited under water, the heated gas presses outward in all directions, forcing the surrounding molecules of water against their neighbors, which are, in turn, propelled forward with great violence. This effect continues until the back pressure of the liquid medium equals the now reduced pressure of the gas due to its expansion in the space vacated by the displaced water, which is likewise to some extent compressed by the action of the gas. Though brought actually to a state of rest, the surrounding water is under the influence of great pressure, which by the law of fluids is transmitted equally in all directions. When a vessel is sufficiently near the explosion to be struck by the water which has been so violently disturbed, it will act upon her like a huge projectile, and it is obvious this range will be in proportion to the amount of explosive employed. This, combined with the resistance her hull offers, will also determine the effect produced.

If the charge is too near the surface of the water, the liquid layer above it will not restrain the liberated gas sufficiently to allow of its full power being exerted in other directions, and hence permits its escape into the atmosphere, throwing up the water in its way to a greater or less height, according to the thickness of the layer. The spectacular effect, therefore, afforded by the upheaval of a large and lofty column of water is no criterion of the efficiency of a submarine explosion, but, on the contrary, shows that much of its energy has been expended in the wrong direction. The amount of submersion to give the greatest lateral effect to different charges of explosive has been ascertained by practical experiments. For 100 lb. of gunpowder, it is stated to be 10 ft., while for the same quantity of guncotton it should be 15 ft. As the charge employed against the Resistance was 90 lb. of guncotton placed 10 ft. below the surface, it is probable that some loss of power was sustained in the manner we have indicated. At a greater depth also the charge would have been to some extent under the vessel, where its explosive effect would have been more severe, and where the construction of the hull cannot be as strongly fortified with coal as was the case in the Resistance. We are unable to state why a depth of 10 ft. was selected on this occasion; but it may be due to the fact that up to a late date most of our locomotive torpedoes have not carried a larger charge than 40 lb. of guncotton, and are usually run at 10 ft. below the surface.

Considerable stress has been laid on the fact that in this experiment the charge was in actual contact, and yet did not effect complete penetration. It is even gravely asserted that an actual torpedo would have rebounded a certain distance before explosion took place, and this would diminish its effect. In the first place, the detonation of guncotton is practically instantaneous, so that impact and explosion would be simultaneous. We are hardly prepared to allow an inch rebound, but will concede that until actual proof convicts us of error. In the second place, it is possible that a distance of three or four feet between charge and ship would rather augment than diminish the effect produced in the case of such an explosive as guncotton when sufficiently immersed. It is possible the intervening water thrown against the side of the ship would do more damage than the gas liberated in actual contact. At any rate, experiments some years ago with smaller quantities of both dynamite and guncotton showed that when exploded 4 ft. from the bottom of a ship, enormous damage was inflicted on her.

Although it is generally estimated that guncotton is about four times more powerful than gunpowder, this does not appear to hold good under all conditions; while, on the other hand, for certain purposes, ten times the amount of gunpowder would not produce the same result. This is proved by the ease with which the strongest chain cable and wire rope can be ruptured by a small charge of guncotton, which even more than ten times the amount of gunpowder could not accomplish. This is due to the peculiar shattering action of detonated guncotton, which the slower burning substances does not possess, its characteristic being more of the nature of a push than a blow. Taking into consideration the method in which the hull of the Resistance had been strengthened for this experiment, and the exact locality chosen for the explosion, it is probable that less than twice the amount of gunpowder would have caused a more complete breach through the coal protection. The torpedo is stated to have had everything in its favor; whereas, in our opinion, all the advantages were on the side of the ship. The attack was made at her strongest point, where the coal was specially disposed, and her shape under water lent no assistance to the explosive. To assume from this that if a similar torpedo struck lower down, or further aft, or against the propeller, the ship would still have "her offensive powers not materially impaired," is to express an opinion with which few will be found to concur.

Under the alternative circumstances mentioned, half the amount of explosive might practically disable the vessel, though her flotation need not be overcome. Whitehead torpedoes need not necessarily be limited to a depth of 10 ft., as by slightly strengthening their construction they could be run 20 ft. below the surface. We presume it will be allowed that this would increase their destructive power, especially in the vicinity of engines and boilers, which now occupy so much space. In a similar manner there is no difficulty in increasing the charge of a locomotive torpedo to a point at which it becomes irresistible, whatever system of internal protection may be devised. This has, in fact, been going on for some time; more than one nation possesses torpedoes armed with 100 lb. of guncotton, and if we do not, it is simply because former experiments led us to believe sufficient damage would be caused by a less quantity. We can only consider that disproved on demonstration by further trials under conditions less favorable to the ship, and we venture to predict some delusions will then be dispelled which this particular experiment seems to have occasioned.

TORPEDO EXPERIMENTS AT PORTSMOUTH—DAMAGE DONE TO THE PORT SIDE OF H.M.S. RESISTANCE.

Before Judges McKennan and Acheson of the United States Circuit Court for the Western District of Pennsylvania, at Pittsburg, Pa., No. 16 of November term, 1886, a question arose as to whether a steel wire brush for cleaning castings, and a steel wire brush for cleaning boiler flues, was an infringement on what is generally known as the Wright patent, No. 59,733, and the reissue, No. 2,598, owned by Joseph McArthur, of New York city.

The Wright patent consists of a wooden block with a series of pairs of holes. A bundle of wire splints is doubled and the ends inserted in the holes, being held by the wooden bridge between the holes and by a wooden back screwed to the block.

Joseph H. Davis, of Sewickley, Pa., the defendant, under his casting brush patent, No. 232,600, the construction of which consists in the doubling of the wire splints and inserting in one hole of a wooden block, and fastening by means of weaving a wire through the loop, the wire being held in place by a wooden back fastened on by driving wrought iron nails through the block and back and clinching on the back, thus making the block and back practically inseparable.

The Davis flue brush patent, No. 181,416, is made by sticking the wire splints through holes in an iron cylinder, there being no wood about its construction.

Several cases had been tried in other States involving the validity of the Wright patent, which had resulted in Mr. McArthur's favor, but after exhaustive argument in the case at Pittsburg, Pa., the court held the Davis brush not to be an infringement on the Wright patent.

The question of how long treatment should be continued in a neurotic case when no evident benefit is produced has recently been raised in a Hamburg law court. A medical man, says theLancet, having as a patient a merchant suffering from "nervousness," treated him by galvanism. Altogether he galvanized him 445 times, but the nervousness did not disappear. Then came the matter of fees. The sum claimed was $556. The merchant disputed this on the ground that the treatment ought not have been continued so long, as it was not producing any benefit. The court referred the matter to the medical board, which gave as its opinion that the doctor ought to have asked the patient, after some fifty sittings, whether he would like to continue them, as it was doubtful whether the treatment was doing any good. The court, however, declined to accept this view, holding that it was for the patient to say when he had tried the treatment as long as he was disposed to pay for it, and so gave judgment for the full amount claimed. This judgment seems to accord with the principle that applies to newspaper subscriptions. A man must pay for his paper as long as he takes it from the post office.

In former issues of theScientific Americanwe have given illustrations and detailed descriptions of the pneumatic dynamite gun invented by Lieutenant E. L. Zalinski, of the U. S. Artillery Corps. This gun, it will be remembered, was designed to throw a projectile loaded with dynamite or nitro-glycerine by means of compressed air; and so successful were the experiments carried on with it at Fort Lafayette, under the supervision of a board of naval experts, that Congress eventually appropriated $350,000 for building a swift torpedo boat, large enough to go to sea, and to be armed with three of these guns. Contracts for this boat have been signed with the Cramps.

The upper view in the accompanying engraving is a longitudinal vertical section, the lower one being a plan view. The following details regarding the boat we take from theSun. The boat will be 250 ft. long, 26 ft. beam, and will draw 8 ft. of water. Her displacement will be about 800 tons. The engines will be of the triple expansion type, of the best known design, and the guaranteed power will be 3,200. She will be propelled by twin screws, and it is expected that the guaranteed speed of 20 knots an hour will be exceeded.

The three dynamite guns are to be placed side by side, at the elevation indicated in the upper view. They are to be fired in their places, but their range can be varied by increasing or diminishing the charge of air let in behind the projectile. An extreme range of one mile is put down in the contract, and the weight of gelatine to be thrown is 200 pounds; but the guns, as now building, will throw 400 pounds instead of 200 pounds, and the effective range will probably be about two miles. Air chambers and compressors of sufficient size and power are provided to enable fifteen shots to be fired to the distance of one mile without stopping; but if the boat were heading for the enemy at full speed, thirty shells could be thrown before the air would be exhausted and the cruiser obliged to turn tail. Thirty shells would mean the explosion of 12,000 pounds of nitro-glycerine about the enemy.

In fixing the gun permanently in its place, the designer has followed out the old idea of making the ship simply a floating gun carriage. The new British cruiser Polyphemus is built on the same idea, and there are other floating gun carriages. In this cruiser the firing is entirely under the control of the officer in the pilot house. He has simply to head his boat for the enemy, dash ahead at full speed, and blaze away. The trained pilot, even in the excitement of battle, would steer his ship instinctively, so there would be little trouble with the aim, except, perhaps, in getting the range.

Each gun can be fired once in two minutes, or the three successively in two minutes.

The new cruiser has a freeboard of about four feet above water. This is quite enough to enable her to travel anywhere along the coast. She carries enough coal to travel 5,000 miles at 12 knots an hour. This would take her about 700 miles at full speed. She could probably turn a complete circle of a radius of twice her length in between two and three minutes. She can carry 100 or even a much greater number of torpedoes with her when going on a cruise. To show how she compares with the best of the latest English built torpedo boats, it may be said that the Destructor, built for the Spanish Government, carries but ten torpedoes, although she has five tubes to fire them from, and this is the usual number carried. The range of the best of these foreign torpedoes is 600 yards, under the most favorable circumstances, and in a seaway not more than 100 or 200 yards. The exploding charge is 75 pounds of gun-cotton, an explosive that is exceedingly inefficient when compared with nitro-glycerine.

The new boat will also be armed with the usual rapid-firing guns which are placed on foreign torpedo boats. These are to be used in battle with craft like herself and small boats. It is expected that she will be finished in six months.

TORPEDO BOAT ARMED WITH PNEUMATIC DYNAMITE GUNS.

Perceiving a common snail,Helix aspersa, crawling up the window blind one evening, it occurred to me to try what it could draw up perpendicularly. Accordingly, I attached to its shell four reels of cotton, fastening one after the other until I ascertained that a greater load would exceed the limit of its strength. I then weighed the entire load, and found that it weighed 2¼ ounces, while the snail weighed only ¼ ounce. Thus it was able to lift perpendicularly nine times its weight. I then made an experiment with a larger snail, weighing one-third ounce, the load being composed chiefly of the same material as the last, but so placed as to be drawn in a horizontal position on the table. Reels of cotton to the number of twelve were fastened to it, with a pair of scissors, a screw driver, a key, and a knife, weighing altogether seventeen ounces, or fifty times the weight of the snail. The same snail when placed on the ceiling was able to travel with a weight of four ounces suspended from its shell. I next tried it on a piece of common thread, suspended and hanging loose with another snail of its own weight, which it carried up the thread with apparent ease. After this I tried it on a single horsehair strained in a horizontal position, but it had then enough to do to crawl over this narrow bridge without a load.—E. Sandford, in Zoologist.

The production of absolute black by a pigment or surface coloration has been shown by Chevreul to be an impossibility. No substance is known that does not possess the power of reflecting light to some extent. If paper is blackened, its surface will reflect rays that can act powerfully upon the sensitive plate in a camera, even if the eye, by convention and association, would determine it to be actually black. The same is to be said of black silk and velvet. The latter, more than any other substance, approaches real black. It is an object of common observation that all colors show much more strongly in velvet than in any other material. The reason for this is that, owing to the depth of the pile, the light undergoes multiple reflection. The percentage of white light is diminished with each reflection, and the colored rays become less and less contaminated with those of other hues. The same reasoning applies to black velvet. The light by multiple reflection from its substance is more and more absorbed, and the familiar intense black is the result. A piece of this material, placed upon cloth or silk, always appears, and is, the blacker. In choosing velvet for such experiments, care must be taken not to use a blue black. The dead black is the proper one to select.

CHEVREUL'S BLACK.

Black being the absence of color is producible by excluding light. The production of the velvet black, we have seen, depends on the mechanical texture of the goods. Nothing is so black as a perfectly dark room. Carrying out these principles, Chevreul devised the wonderfully ingenious way of producing a true black which we illustrate.

He lined the interior of a box with black. Pigment, black silk, or black velvet may be used. In the cover of the box he made a hole, not too large, but bearing a certain ratio to the area of the cover. The size should not exceed one-tenth this surface. The spot thus produced reflected no light, as there was no surface. The interior of the box, by color and shadow, was prevented from reflecting any light, so that absolute blackness resulted. The blackest velvet or silk placed alongside of this spot appears lighter in color.

In constructing the apparatus illustrated, a famous proverb was selected as a theme, in which a certain personage is stated not to be so black as he is painted. The author of "English as She is Spoke" renders this proverb, "He not so devil as he is black." The blackness of this image is absolute.

A pasteboard box is lined with black silk or velvet, and any desired figure is cut through the cover. This may then be painted as black as possible, or before the figure is cut out, silk or velvet may be pasted over it, and the figure cut through pasteboard and covering together.

Then, on putting the cover in place, holding the box so that a side light will fall upon it, thus preventing direct access of light rays to the interior, the figure will stand out strongly black against a background which, but for the contrast, would itself be pronounced absolutely black.

To apply the most rigorous test, a member of the Society of Amateur Photographers of New York made a photograph of such a box. A carbon B dry plate was used, with thirty-five minutes' exposure, with stop f-30. The result was a negative perfectly transparent where the figure came, but strongly affected by the black box cover. Part of the cover was coated with black silk and part was painted, but both reflected light enough to produce a full photograph upon the plate.

A most interesting application of this principle on the large scale has been made of late years, especially by E. J. Marey, in the photography of moving animals.2With Chevreul's black as a screen, a plate can be exposed unaffected by the background, and will reproduce objects moving across the space with perfect fidelity.

Recently we had an opportunity of going over the grounds of the forthcoming American Exhibition at Earls Court. The site is comprised in the triangle between Earls Court, West Brompton, and West Kensington stations, and is thus extremely well situated for easy access from all parts of London. The area that will be covered by the exhibition is about twenty-three acres, eight of which are on one and fifteen on the other side of the West London line, an iron bridge over the railway connecting the two portions. Although the work has been going on for some time, little is as yet seen of any building, the operations up to the present having been confined mostly to earth works, leveling, and draining. The land to be occupied by the exhibition might almost be called virgin soil, and all the drains had to be put in by the company. A good deal of soil has been moved, and some artificial mounds of considerable extent have been thrown up. In that portion of the exhibition which will be illustrative of the "Wild West," a large arena and a grand stand capable of seating 25,000 persons are in course of construction. The feature of special interest to engineers is, however, on the other side of the grounds, where the main building for the reception of the machinery and other exhibits is now being erected. The main hall has a frontage of brickwork 240 feet long, but the rest will all be constructed of iron and glass. The total length of this hall is 1,200 feet, and a special feature in its construction is the employment of old steel rails for the columns, purlins, and rafters, on a plan devised by Mr. H. G. Wynne, the engineer to the company. The whole of the framework is thus made out of old rails, the only portions specially made for the purpose being the cast iron sockets for the columns, cast steel shoes for the connections between purlins, rafters, and columns, and tie bars, which are made of ordinary round iron. There will be six bays of 30 feet each, and one bay of 60 feet. The columns are formed by two rails, riveted together with their flanges, so as to present a cross in transverse section. These are placed into cast iron sockets, which are set upon cement piers sunk in the ground. The outermost columns for the first and last spans are provided with struts, also formed out of rails, fixed to a sleeper, connecting the bottom of the strut with the foot of the column, this provision being made to provide against lateral strains; but the columns of the intermediate spans have no struts. The rafters are also made of rails, placed with the flanges uppermost, those for the short spans being in one length, but those for the long spans being fastened together by fish plates. The usual length of rail employed for the columns is 18 feet and 24 feet. There is a fall in the ground of about 2 feet to both sides from the middle of the building. To avoid the necessity of employing columns of different lengths, the ridge of the roof is carried parallel to the ground, and will therefore also show a fall of 2 feet on each side of the middle. This will be hidden by a loose louver, which is placed all along the ridge, so that the outline of the roof will appear straight and horizontal. The sides of the building will be of galvanized corrugated iron.—Industries.

Petroleum In Egypt.—At Jemsah, in Egypt, in boring for petroleum, ozokerite, or solid petroleum, has been found at a depth of 365 feet, and 15 feet lower a close grained coral has been struck. At another boring, slight traces of gas and oil have also been found.

A spark arrester has been patented by Mr. John C. Albrecht, of Columbus, Ga. Combined with a draught pipe is a cone with curved volutes, and in its center and underneath it an inverted cone, with spark pockets, and other novel features, the sparks being returned to the fire box, the invention being an improvement on two former patented inventions of the same inventor.

A steam condenser has been patented by Mr. John McIntyre, of New York City. It is cylindrical in form, a central perforated or slotted casing being used in connection with the cooling pipes, with a regulating valve to open or close the perforations or slots, in such way that the cooling effect will be more instant and the temperature of the cooling parts more equal than in ordinary condensers.

A car coupling has been patented by Mr. George W. Giles, of Buffalo, West Va. In connection with a suitable drawhead, a weight and pin are joined by a flexible connection, the weight being adapted to overbalance the pin, and the weight being projected into the path of the drawbar, so that the entering drawbar will raise the weight, and thus permit the pin to fall by its own gravity into coupled position.

A car coupling has been patented by Mr. Wesley E. Roberts, of Hartford, Ky. The coupling link consists of a straight bar, with a wedge shaped pointed lug at each end, a spring being fastened to the under side, and the coupling being effected by an arm dropping in front of the lug after the link enters the drawhead, the device being simple in construction, and one which can be operated from the side or top of the car.

A mower has been patented by Messrs. James B. Nieth and Charles L. Thomas, of Independence, Iowa. This invention covers a novel construction and combination of various parts of the machine, so that it will operate with less friction than ordinary mowers, while being simple in construction and not liable to get out of order.

A plow has been patented by Mr. Thomas J. Eriom, of Union Church, Miss. It is an improved garden plow, with simple means for adjusting the gauge wheel to regulate the depth of working, and a breast bar for pressure by the operator to increase the propelling power and to give the plowman a better control of the plow, with other novel features.

An attachment for elevator doors has been patented by Mr. Edward P. Walker, of Kansas City, Mo. It is an attachment designed to effect by the movement of the elevator car the automatic operation of the doors of the shafts, so that the elevator man is relieved of this duty.

A saw gummer has been patented by Mr. Eli Rogers, of Fulton County, Ind. The invention consists of a cam lever operating a spring arm on which is pivoted a tool holder, making a device which is simple in construction, durable, and effective in operation.

A hame has been patented by Mr. John E. James, of Mossy Creek, Va. It is so made that the shoulder of the horse will not be affected by heavy jars, and the hames may not only be fitted to any length of collar, but the point of draught may be shifted, so that the draught will be brought to the proper point.

A tongue support has been patented by Messrs. Charles W. Van de Mark and Calvin Moore, of Clyde, Kansas. The construction is such that the tongue may be supported so as to relieve the team of its weight, and the devices for supporting it are simple, inexpensive, and not likely to get out of order.

A fence post has been patented by Mr. John J. Kimball, of Naperville, Ill. Combined with side strips are rivets, spacing strips arranged between the side strips, clips formed with apertures, and staples arranged to pass through the apertures, making a cheap, durable, and efficient post for barbed wire fences.

A combined chair and lounge has been patented by Mr. Gustavus Hamel, of De Soto, Mo. The parts are so arranged that the back of the chair may be adjusted to any angle desired, and the attachment constituting the foot rest or foot of the lounge may be disposed beneath the main seat of the chair when not in use.

A harmonic keyboard for violins has been patented by Mr. James F. Poage, of La Plata, Mo. It is designed to enable the performer to produce harmonic high tones without great difficulty, and is attached to the neck of violins of the usual construction, the keyboard being a combination of pivoted finger keys with a pivoted stop plate.

A rein holder has been patented by Mr. William Tennison, of Mount Vernon, Ind. This invention covers an improvement in rein holders consisting of a skeleton frame adapted for attachment to a harness or for support upon a horse's back, and used for the purpose of supporting the reins out of the way of the animal's tail.

A collar button has been patented by Mr. Leopold Baer, of San Francisco, Cal. To the center of the button back is secured a tubular shank in which is a spiral spring, there being a knuckle joint by which a tongue may be held in three different positions, the device making a conveniently working button for holding the necktie in place.

A bridle has been patented by Mr. Benjamin S. Seaman, of Corning, N. Y. The cheek plate is formed with studs on which the blind sheet is adapted to be placed, and secured by a key plate constructed to engage with the studs, the cheek loop being secured to the cheek plate with the same stud plate and key plate which hold the blind.

A machine for bending carriage thills has been patented by Mr. Thomas E. Montague, of West Lorne, Ont., Canada. It is for bending wooden shafts or thills for buggies, sulkies, carriages, and other vehicles, and covers a novel construction and combination of parts and details, whereby thills of greater or less thickness can be bent, the machine operating very rapidly and automatically.

A nut lock has been patented by Mr. Jeremiah C. Butler, of Lexington, Mo. The construction is such that the key may be drawn off the bolt by the nut, and need not be bent out straight into the keyway of the bolt to prevent its locking portion engaging in the recesses of the nut as the latter is being turned off the bolt, the key needing only to be bent very slightly for adjustment into locked or unlocked position.

A trousers stretcher has been patented by Mr. Charles E. Ray, of San Francisco, Cal. The trousers are clamped below the waist band and at the bottom, the clamp at the waist band attached to a spiral or rubber spring, secured in fixed position at one end, while to the clamp at the bottom is attached a strap by which tension can be placed upon the trousers, and permanently maintained.

A log dog has been patented by Mr. Eugene H. Allman, of Mobile, Ala. It is made of heavy wrought iron, with a flat body portion, and having end points or fangs, and is applied to the chain by shouldered clips, all extra chains and dogs being dispensed with by its use, and when used on endless chains it being only necessary to point the logs in the logway, when the dogs take hold and bring them up.

An electrical weighing scale has been patented by Mr. Willis M. Hunt, of Glen Gardner, N. J. Combined with feeding hoppers arranged above the scale pan are valves operated by connection with the foot lever for discharging the hoppers, and combined therewith is an electro-magnetic holding and releasing device, which automatically stops the feed when the scale beam is tipped.

A boot or shoe stretcher has been patented by Mr. Lloyd Nottingham, of Norfolk, Va. Centrally pivoted levers have apertures in their lower end to receive pins with rounded outer ends, and above the pivotal point is an adjusting screw to separate the levers in stretching the boot or shoe, the levers being held apart by locking pieces, the device being simple, strong, and easily operated.

A combined bench and ironing table has been patented by Mr. Daniel H. Weller, of Boyertown, Pa. Combined with a reversible board with covered socket boxes are supports hinged to the legs of a bench, with other details, to make a desirable piece of furniture to serve the two purposes of a seat and a table to iron upon, with compartments for keeping the cloths used in ironing.

A window frame and sash has been patented by Mr. John E. Jones, of New York City. The construction is such that the sashes when closed are to all intents and purposes air tight, and wear and friction are removed from the packing strips, so the sashes may be raised and lowered without injury to the packing, the invention being an improvement on a former patented invention of the same inventor.

A tug fastener has been patented by Mr. Daniel T. Chambers, of Mansfield, Ohio. It is in the nature of a divided button, one portion integral with a shank that goes in the end of the single tree, and the other formed of two limbs, one completing the periphery of the button and the other extending up parallel with the shank and forming a part of the neck beside the button on which the trace is contained.

A tug fastener for single trees has also been patented by the above inventor. It consists of a tilting latch hinged upon a horizontal axis at or near the end of the single tree, with one hub adapted to lie longitudinally with the single tree and the other to project upwardly at about a right angle thereto, making an easily operated device for fastening the traces to a single tree.

A plaster fastener has been patented by Messrs. Forest M. Lampson, Alpheus M. Laning, and George W. Hogben, of Ripon, Wis. It consists of a metallic washer formed of thin sheet metal, slightly convex, and provided with a countersink in the center, formed by the process of stamping, the device being intended to secure plastering loosened by shrinking of the lath, etc., before it becomes cracked and disintegrated.

A combined towel, hat and paper rack has been patented by Mr. Elbridge L. Scribner, of Amesbury, Mass. (P. O. Box 98). It is a simple, inexpensive, and efficient device, consisting of a frame formed of end pieces of wood, connected by wooden slats on the back, and supporting three rods of metal or wood for receiving the articles to be held, the lower rod being designed for receiving a roller towel, and the upper rod being offset or cranked for convenience in placing articles on the lower rods.

Mineral Resources of the United States, Calendar Year1885. Washington: Government Printing Office, 1886. Pp. 576.

This is a carefully compiled volume, giving the statistics for mineral products in the United States. Coal, coke, petroleum, and natural gas are first treated of; the metals, from iron to zirconium, come next. Under aluminum the work of Col. Frishmuth, of Philadelphia, and of the Cowles Smelting Company, of Cleveland, are noted. In view of the demand for zirconium pencils for the oxyhydrogen light, the section on the sources and preparation of the oxide, by Mr. David T. Ray, is of special interest. Other subjects treated are structural materials, abrasive materials (buhr stones, etc.), precious stones, fertilizers, glass materials, and, under many other headings, a complete review of the titular subject appears. We also note a section of much interest on mineral paints, by Mr. Marcus Benjamin, F.C.S. In it the preparation of barytes as an adulterant for paints is described at some length. In some instances an elaborate explanation of the classification of paints as adopted is given. In other cases it is entirely omitted. The first system is certainly preferable. A very full index closes the work. It can be had on application to the Director of the United States Geological Survey, Washington, D. C., the cost of printing and binding (40 cents) being at the same time remitted.

The charge for Insertion under this head is One Dollar a line for each insertion; about eight words to a line. Advertisements must be received at publication office as early as Thursday morning to appear in next issue.

Best tempering fluid known—Mercury, potash, and hydrochloral. $2.00 per gallon. Samples, 25c. Address Chemical Works, New Albany, Ind.

Hodges' universal angle union makes pipe connection at any angle. Rollstone Machine Co., Fitchburg, Mass.

To makers of water wheels, current wheels, and horizontal turbines—Please address W. H. Garlick, Calumet, Ohio.

Sphero! A new and original game; an out-door sport; unlike any other. Apparatus of wood, simple, inexpensive. Packed like croquet, and cost to manufacture about the same. Patent pending. Rights, etc. Address J. M. Hughes, Brooklyn P. O., N. Y.

The H. W. Johns Manufacturing Co., 87 Maiden Lane, N. Y., will send to any address in the United States, postage prepaid, a trial package of ¼ pound of asbestos wick packing and 1½ pounds of asbestos piston rod packing, on receipt of one dollar; or ¼ pound of asbestos wick packing and 3½ pounds of asbestos piston rod packing, on receipt of two dollars. Give address in full—name, town or city, county, and State. The H. W. Johns asbestos packings are the best and most economical made.

For Sale—Ivory button works. Large, well lighted building; 20 H.P. engine; capacity, 200 gross per day; doing splendid business; plenty of cheap labor. Price, only $3,000. Address T. Bergy, Caledonia, Mich.

Wanted—A pushing man, capable of taking charge of a shop for building engines. A fine chance for a skilled mechanic. Address, with references, etc., lock box 17, York, Pa.

Blake's Improved Belt Studs are the best fastening for Leather and Rubber Belting. Greene, Tweed & Co., 83 Chambers St., New York.

Wanted—Tool agents in shops. Outfit free. E. H. Randall & Co., 154 Lake St., Chicago, Ill.

Link Beltingand Wheels. Link Belt M. Co., Chicago.

TheRailroad Gazette, handsomely illustrated, published weekly, at 73 Broadway, New York. Specimen copies free. Send for catalogue of railroad books.

Anti-magnetic shields—an absolute protection from all electric and magnetic influences. Can be applied to any watch. Experimental exhibition and explanation at "Anti-Magnetic Shield & Watch Case Co.," 18 John St., New York. F. S. Giles, Agt., or Giles Bro. & Co., Chicago, where full assortment of Anti-Magnetic Watches can be had. Send for full descriptive circular.

Woodworking Machinery of all kinds. The Bentel & Margedant Co., 116 Fourth St., Hamilton, O.

Guild & Garrison's Steam Pump Works, Brooklyn, N. Y. Pumps for liquids, air, and gases. New catalogue now ready.

Concrete patents for sale. E. L. Ransome, S. F., Cal.

The Knowles Steam Pump Works, 44 Washington St., Boston, and 93 Liberty St., New York, have just issued a new catalogue, in which are many new and improved forms of Pumping Machinery of the single and duplex, steam and power type. This catalogue will be mailed free of charge on application.

Presses & Dies. Ferracute Mach. Co., Bridgeton, N. J.

Nickel Plating.—Sole manufacturers cast nickel anodes, pure nickel salts, polishing compositions, etc. $100 "Little Wonder." A perfect Electro Plating Machine. Sole manufacturers of the new Dip Lacquer Kristaline. Complete outfit for plating, etc. Hanson, Van Winkle & Co., Newark, N. J., and 92 and 94 Liberty St., New York.

Iron Planer, Lathe, Drill, and other machine tools of modern design. New Haven Mfg. Co., New Haven, Conn.

Supplement Catalogue.—Persons in pursuit of information of any special engineering, mechanical, or scientific subject, can have catalogue of contents of theScientific American Supplementsent to them free. TheSupplementcontains lengthy articles embracing the whole range of engineering, mechanics, and physical science. Address Munn & Co., Publishers, New York.

Planing and Matching Machines. All kinds Wood Working Machinery. C. B. Rogers & Co., Norwich, Conn.

Billings' Drop Forged Steel C Clamps. Drop Forgings, all kinds. Billings & Spencer Co., Hartford, Conn.

Curtis Pressure Regulator and Steam Trap. See p. 45.

Chucks—over 100 different kinds and sizes in stock. Specials made to order. Cushman Chuck Co., Hartford, Ct.

The Improved Hydraulic Jacks, Punches, and Tube Expanders. R. Dudgeon, 24 Columbia St., New York.

Hoisting Engines, Friction Clutch Pulleys, Cut-off Couplings. D. Frisbie & Co., 112 Liberty St., New York.

If an invention has not been patented in the United States for more than one year, it may still be patented in Canada. Cost for Canadian patent, $40. Various other foreign patents may also be obtained. For instructions address Munn & Co.,Scientific Americanpatent agency, 361 Broadway, New York.

Veneer Machines, with latest improvements. Farrel Fdry. Mach. Co., Ansonia, Conn. Send for circular.

Tight and Slack Barrel Machinery a specialty. John Greenwood & Co., Rochester, N. Y. See illus. adv., p. 28.

Walrus, Bull Neck, and Buffalo Leather for polishing emery, glue, composition, Polishers' Supplies. Greene, Tweed & Co., New York city.

A clergyman, after years of suffering from that loathsome disease, catarrh, and vainly trying every known remedy, at last found a prescription which completely cured and saved him from death. Any sufferer from this dreadful disease sending a self-addressed stamped envelope to Dr. Lawrence, 212 East 9th St., New York, will receive the recipe free of charge.

Lick Telescope and all smaller sizes built by Warner & Swasey, Cleveland, Ohio.

Send for catalogue of Scientific Books for sale by Munn & Co., 361 Broadway, N. Y. Free on application.

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