IXTIDES

Fig. 54. Science of kite-flying

"The first thing a beginner in the science of aeronautics will want to know is, 'Why does the kite or machine lift itself off the ground?' If you take a kite and hold it in an inclined position, the wind on the lower side will have a tendency to blow it backward; but as it is held by the kite string, this movement is impossible, and so it is inclined to rise in the air (seeFig. 54). If we construct a large plane and equip it with a motor operating a screw which pushes or pulls the plane along through the air, the result is the same as if the plane were anchored, and the wind hits the lower surface of the inclined plane, thus forcing it up. Also, we find, within certain limits, the more you incline a plane the more lift or upward thrust will it give; but it will take more powerto drive it through the air, and the faster the plane is driven through the air the less surface is required to support the weight. A matter of great importance in the construction is the shape of the plane, and the shape of the vertical section through the same. The shape of these planes has been explained in Figs.43and44, and the reasons were given why these shapes were considered the proper ones for the purpose.

"It does not follow," said Mr. Gregg, "that all kites should have the same kind of a surface or plane, though the flat planes of the toys of our school days were all of the flat surface kind; these being of various shapes and sizes from the lozenge to the square, bow top, octagon, and many others, according to the whim or skill of the maker. One of the conditions of these planes or flat kites, was that each one must have at least one tail attached to the bottom of it. This tail was flexible, simply a piece of string having paper similar to 'curl papers' tied to it at intervals. The tail was a necessity, for without it the equipoise would be impossible. In China and Japan, where the natives have been kite-flying for more than twenty centuries, they make kites that fly and maintain the aerial equipoise without having tails hung to them, no matterwhether the shape be that of a dragon, a lion, or an eagle.

Fig. 55. Box kite

"A kite is simply an aeroplane on a small scale, and should be considered as such, as it has a fixed fulcrum in the belly band, a constant pressure when flying, and an angle which is varied in proportion to the load it may have to carry. The common kite is easily made, but it does not always fly as desired; for it seems almost impossible to make two kites that will fly in the same manner under similar conditions. Box kites are the most reliable, and not so very difficult to make, as you will discover by examining Figs.55,56, and57and following the directions I give you. First, procure four straight strips of light wood, preferably spruce, 2 ft. 6 in. by3⁄8in. by1⁄8in.; these dimensions should be full (seeFig. 55.) Obtain also four other pieces, each 1 ft. 71⁄2in. long, but1⁄16in. wider and thicker than the foregoing, and halve their ends to a depth of1⁄8in. by1⁄4in., in order that when the false end A (Fig. 56) is tightly bound on, these cross sticks will firmly grip the long pieces edgewise,the sides of the cells being indicated by the dotted lines. The long sticks should be notched at a distance of 4 in. from their ends to receive the forks of the cross sticks.

Fig. 56. Making a kite

"The width of the cloth or paper cells should be 8 in., and they should be separated by a distance of 1 ft. 1 in. or 1 ft. 2 in., their edges being bound with fine twine. The easiest way to make the cells is to cut two strips of the material, 10 in. wide and 4 ft. 81⁄2in. long. Turn over the edges1⁄2in. along each side, and insert fine strong twine! If paper is used, glue the fold; if cloth, stitch the hem. When completed, either glue or stitch the ends of the strip with a3⁄4in. lap, so as to form a continuous band. By folding, divide this accurately into four equal parts and at each of the creases glue one of the long sticks edgewise (seeFig. 56). When dry, the whole can be put together and the flying line attached, without a bridle, as inFig. 55. For additional clearness an enlarged detail of one end of the kite is shown atFig. 57.

Fig. 57. Single box kite

Photograph by Brown BrosMaking Kites"Box Kites Are the Most Reliable, And Not so Very Difficult to Make"

Photograph by Brown Bros

Making Kites"Box Kites Are the Most Reliable, And Not so Very Difficult to Make"

"It is advisable in all cases to make the cross pieces a trifle too long, to insure their straining the band tightly. They may also be shortened by cutting away the shoulder formed by the halving.

"These kites are easy to fly. Avoid an enclosed space, where the wind whirls in invisible eddies; having let out 20 yds. or 30 yds. of line, get some one to throw up the kite in the usual fashion. If several large kites are sent up in tandem, steel wire should be used.

Fig. 58. Square cellular kite

"Another kind of a kite, known as the cellular kite is shown inFig. 58. This is made by forming two square frames N. O., divided into nine compartments each and connected together by a light rod atr, the fulcrum or string being at P, the air pressure at T. The whole forms a good, strong kite, but it is not able to carry much weight, on account of the equipoise being self adjusted in accordance withthe constant pressure and surface. The equipoise is due to the current being cut by the edgesa a´, and diverted into the cellular divisions of each area. This being the case, any upward or downward tendency ofa a´, would be counterbalanced by the effect on the other side and the kite would naturally adjust itself on the opposite side. We are not dependent upon any particular shape for obtaining a good serviceable kite—like the plane made kite, the cellular one may be of any shape. I show you one here, atFig. 59, having a circular rim, with thin tubes inserted in such a manner that the current of wind will rush through when the machine is in the air. The two portions, A and B, are held together by a rod in a similar manner to the square kites, and the cord or fulcrum is fastened to the rod at R.

Fig. 59. Circular cellular kite

"A number of kites may be sent up at once, all attached to the same string, if properly adjusted. Here are six square cellular kites looped together, shown atFig. 60. They may be made of any suitable size, but need not be all of one size, though each pair would be better if made the same size.They may be looped up, as shown, and the point S may be loaded lightly; it will help to steady the kite and keep it from swaying.

Fig. 60. Group of kites

"A peculiar kite, called 'a war kite,' is very popular in some parts of Europe, and in some parts of our country also. It is easily made and gives good results. It is on the principle of the 'cellular' or 'box' kite, being cubical or box-shaped, and, when used for carrying weights, usually has several cells built together, or several kites may be coupled when a heavy load, such as that of a man, is to be raised. These kites are made of light wood or cane covered with nainsook or fine cotton, and strengthened with cross pieces which hold the frames tight and keep the kite in shape. They can be taken to pieces and the covering material rolled up so that they occupy very little space. Two forms of box kites are shown in Figs.61 and 62, and it will be seen that an attachment is made each side of the frame. This is fine steel wire, very light compared with its strength, wound on a drum by means of a small engine. Large kites of the ordinary form can be used for the samepurpose, but their lifting power is not equal to that of the box kite. A small box kite is used for taking photographs, a camera being carried by a separate wire connection to the attachment wire, and the shutter released at the proper time by an ingenious arrangement, similar to the pieces of paper called 'messengers' which boys used to send up on the cords of ordinary kites. This kite is a little more expensive to make than most of those shown, but it gives an excellent result when properly handled.

Fig. 61. Sextuple kite Fig. 62. War kite

"In making kites of any kind, the lightest materials consistent with sufficient strength, should be employed. The frames should be split bamboo or cane. The joints may be lashed together with fine wire or silk thread, and the envelope in each case should be fine silk or similar material thatwould be close, light, and strong. These qualities, in all sorts of kites and aeroplanes, are absolutely essential to accomplish the best results.

"Before leaving the subject of aeronautics, I think it would not be amiss to tell you something of bird flight. There are different modes of flying, just as men have different gaits in walking or running.

"Rapid wing movement does not always imply speed in flight, any more than does rapid leg movement imply speed in walking or running. With us it is the length of the stride that tells ultimately. What tells, correspondingly, in the flight of the bird is not known.

"Speaking broadly, long-winged birds are strong and swift fliers; short-winged birds are feeble in flight. When we consider that a cumbrous, slow-moving bird like the heron moves its wings twice per second when in flight, it is evident that many birds have a very rapid wing movement. Most small birds have it, combined with feeble powers of flight. The common wren and the chipping sparrow, for instance, have a flight like that of a young bird.

"What can give one more exquisite pleasure than to watch seagulls swooping round the edgeof a cliff, to see them drift down wind with wings motionless, then suddenly dart downward, turn to meet the breeze, and beat up against it with all their ingenuity and skill?

"The beauty of a ship depends on the way it glides through the water. Watch a liner, and you can see that it is being driven by its screws, but look at a racing yacht: there is no sense of effort whatever. She seems to move like a bird, by natural means.

"Here is the secret of the beauty of the aeroplane. It seems to be completely master of the element in which it moves. It flies with no visible effort and at a little distance one could imagine it endowed with magic power, moving by natural force, like a bird.

"All the early attempts at flying were made on the theory of wing motion, and the failures resulting were doubtless due to careless study of what nature could teach. There was a great deal more to be learned from nature than from mathematics. An examination of the different types of birds testifies, among other things, to their rigid backs, and to the fact that nearly all their bones are hollow and have air cavities. An erroneous deduction had been drawn from this that the hollows were purelyfor the sake of lightness, and that the cavities were for hot air to make the bird light when it wanted to fly. The amount of lightness so obtained, however, was so small as not to be worth consideration. The passages are simply reservoirs for air, and they allow the bird more energy than a less freely breathing animal. The wing of the bird does a double duty: it is an aeroplane and a propeller combined. The valvular action has nothing at all to do with the flight. Some explanation of how a sparrow can rise from the gutter to the eaves may be seen by the difference in the construction of its wings from those of the swallow, which cannot rise from the ground like a sparrow, but has to get initial velocity. The swallow, however, has much more mastery over its movements in the air than the sparrow has. These, and many other things in connection with bird flight, under proper methods of scientific investigation, may show us the whole theory of aviation. I am inclined to think that scientific men will soon be able to solve the problem, and to give us better control of the coming aeroplanes, or even direct their flight by the aid of electric waves or other natural forces.

"In kite-flying, it is well to know something of the wind and its pressure, and, in this connection,the following short table will give some idea of the force exercised on objects in its path: A light air current presses 0.004 lbs. per square foot.

"This last should be the limit, as a kite or aeroplane of any kind will find it hard to manœuvre in a breeze stronger than a moderate gale. Of course, there are winds sometimes that have a velocity of 60 to 75 miles an hour, and a pressure of over 40 pounds to the square foot, but these would prove disastrous to any kind of a flying machine, if it was in action."

"Father," asked Fred, "how can one tell the velocity of the wind, without one of those expensive machines I see at the weather office, an anemometer, I think it is called?"

"I am glad," said the father, "that you have noticed those and other instruments for gauging and foretelling weather conditions. It is an indication that you keep your eyes open when you visit such places, and to learn by observation is almost as effectual as to obtain knowledge by experience.I have in mind a very simple contrivance you can make yourself, for measuring wind pressure from a couple of ounces to four pounds to the foot. I will make a sketch of it, which I am sure you will understand.

Fig. 63. Wind gauge

"It consists of a light pine or cedar wood frame on a strong stand, supporting on a centre two bent wires, carrying at one end a 3-in. square of thin wood, A, and on the other a thin bar of wood, to the centre of which is attached a fine string tied to a spring balance scaled to1⁄8of an ounce and up to 4 ounces (Fig 63). As the square of 3 inches is the 16th of a foot, each ounce on the spring is equal to 1 lb. pressure on the square foot. The latter balance slides in the V-frame at the back so as always to keep the square parallel to the face of the frame, whether the wind is strong or light, and the balance must be slidden in or out until the face of the square is so placed before registering the force of the wind. By attention to this it will register very truly upto 4 lbs., which is the extent of an ordinary spring balance. There is also a front view, a side view, and a bird's-eye view, also one of the bent wires and the 3-inch square. I think this requires no further explanation."

Fred was satisfied with the description of the register and promised to make one at an early date.

The following evening when they were all sitting on the river bank, Fred suddenly asked his father if it was difficult, or costly, to secure patents. He wanted to know, because he had been thinking of making a kite on a new principle—that of a funnel, and he was so sure it would prove a success that he would like to have it patented.

Mr. Gregg thought the scheme rather an ambitious one, but, while he could not see it as Fred did, he determined not to say anything that would be likely to discourage the boy. So he explained, as well as he could, the patent laws: "In order to apply for a patent it is necessary to file in the Patent Office at Washington, D. C., a petition, affidavit of invention, drawings, and specifications, all of which must be prepared in legal form and in accordance with official rules and practice of the office.

"This can best be done by a reliable attorneybut an applicant should understand some of the requirements as well.

"The Patent Office does not require a model to be furnished in order to apply for a patent, but if the attorney is not near enough to see the one made by the inventor, then one should be sent him, unless good photographs and drawings can be supplied.

"Since the drawing attached to the specifications and claims is to be on a sheet of a special size, no attention need be paid to having the original sketches of a uniform size. When ready to apply for a patent, secure as much evidence as possible of the reliability of some attorney you have heard of and consult him about the matter, explaining as much as is necessary for him to prepare an outline that will suffice for a preliminary search through the records in the Patent Office to see that no interference will take place should the application be made.

"This usually costs $5.00, and an attorney often supplies copies of existing patents that look the most like the one in question.

"If it is thought that there will be no interference, the case is then prepared for the examiners, and the application duly made.

"The drawings should be made and lettered, so that the specifications can be written up, including the proper reference to the different parts.

"The drawings should be made upon paper stiff enough to stand in a portfolio, the surface of which must be calendered and smooth. The best kind is patent office bristol, though there is a style on the market printed with margin and headings all ready for use, but the surface is not of the best.

"The size of the sheet on which a drawing is made should be exactly 10 × 15 inches with margin lines one inch from all the edges, leaving a clear space of 8 × 13 inches.

"One of the smaller sides is regarded as its top, and measuring downward from the margin, or border line, a space of not less than 11⁄4inches is to be left blank for the insertion of title, name, number and date, to be put in by the patent officials.

"All drawings must be made with the pen only, using the blackest India ink. Every line and letter, including the signature must be absolutely black.

This applies to all lines, however fine, to shading and to lines representing cut surfaces in sectional views. All lines must be clean, sharp, and solid, and they must not be too fine or crowded.

"Surface shading, when used, should be left very open. Sectional shading should be by oblique parallel lines, which may be about one-twentieth of an inch apart. Drawings should be made with the fewest lines possible consistent with clearness, for the drawings are subjected to photographic reduction, which decreases the space between the lines.

"Shading (except on special views) should be used only on convex and concave surfaces, and there sparingly, or it may be dispensed with if the drawing is otherwise well made.

"The plane on which a sectional view is taken should be indicated on the general view by a broken or dotted line.

"Heavy lines on the shade sides of objects should be used, except where they tend to thicken the work and obscure the reference letters.

"The light is always supposed to come from the upper left hand corner, at an angle of forty-five degrees.

"Imitations of wood or surface graining should not be attempted.

"The scale to which a drawing is made ought to be large enough to show the mechanism without crowding, and two or more sheets should be usedif one does not give sufficient room to accomplish this end; but the number of sheets must never be increased unless it is absolutely necessary.

"Sometimes the invention, although constituting but a small part of a machine, has to be represented in connection with other and much larger parts. In a case of this kind, a general view on a small scale is recommended, with one or more of the invention itself on a much larger scale.

"Letters or figures may be used for reference, but they should be well made, and when at all possible should not be less than one eighth of an inch in height, that they may bear reduction to one twenty-fourth of an inch; or they may be much larger when there is sufficient space.

"Reference letters must be so placed in the close and complex parts of a drawing as not to interfere with a thorough understanding of the same, and to this end should rarely cross or mingle with the lines.

"The illustrations on pages of current topics under the head of new patents show the manner of putting in the reference lines from the letters to the part indicated.

"These are carried out some distance, but if placed on the face of the object where sectioned,a blank space should be left in the shading for the letter.

"If the same part of the invention appears in more than one view, it should always be represented by the same letter.

"Great care should be exercised in the matter of drawings, or they will be returned to the applicant, but, at his suggestion and cost, the officials will make the necessary corrections.

"The time required to procure an allowance of a patent averages from six weeks to two months.

"United States patents are granted for a term of seventeen years, and cannot be extended. The patent remains good whether the invention is worked or not, and no additional payments are required beyond the cost of first taking out the patent. Patents are not subject to taxation. Reissues of patents are granted whenever one is inoperative or invalid, by reason of a defective or insufficient specification, or by reason of the patentee claiming more than he had a right to claim as new, provided the error arose by inadvertence, accident, or mistake, without fraudulent intent. A fee of $30.50 must be forwarded upon application for patent.

"As stated before, a patent is obtained by a petition to the Commissioner of Patents accompaniedby a description, including drawings and a model, when the invention will admit of these. A fee of $15 is required when the application is made, and a further fee of $20 when the patent is issued. Postage on model is at the rate of 1 cent per ounce.

"A patent for a design is granted to any person who has invented or produced any new and original design for the printing of woollen, silk, cotton, or other fabrics; any new and original impression, ornament, pattern-print, or picture to be printed, painted, cast, or otherwise placed on or worked into any article of manufacture; or any new, useful, and original shape or configuration of any article of manufacture, the same not being known or used by others before this invention or production thereof, or patented or described in any printed publication, upon payment of the duty required by law, and other required proceedings the same as in cases of inventions or discoveries. These are granted for three and one-half years, seven years or fourteen years, for which the respective fees of $10, $15, and $30 are paid the government.

"A caveat is a provisional protection to any person who has thought of an invention and desires the time to complete or perfect the same. It is procured at an expense of $10, and runs for oneyear with the permission of renewal from year to year.

"In Canada the patent office is a branch of the Department of Agriculture, and the Minister of Agriculture for the time being is the Commissioner of Patents.

"Any intending applicant for a patent who has not yet perfected his invention, and is in fear of being despoiled of his idea, may file in the patent office a description of his invention so far, with, or without plans, of his own will, and the Commissioner, on payment of the prescribed fee, shall cause the said document, which shall be called a caveat, to be preserved in secrecy, and, if application is made by any other person for a patent interfering in any way therewith, the Commissioner shall forthwith give notice, by mail, of such application to the person filing such caveat, who shall, within three months thereafter, if he wishes to avail himself of the caveat, file his petition, and take the other steps necessary on application for a patent. The application for the patent must be made within one year from the filing of caveat, otherwise the Commissioner is relieved from the obligation of giving notice.

"The following fees are payable: Full feeon patent for 18 years, $60.00; partial fee for 12 years, $40.00; partial fee for 6 years, $20.00; on filing caveat, $5.00; on registering assignment patent, $2.00; for copy of patent, with specification, $4.00.

"The disbursements for filing an application in Great Britain are $25.00; France, $20.00; Germany, $5.00, and $7.50 before issuing patent; Australia, $20.00; Russia, $75.00; British India, $20.00. The German and French patents cover not only Germany and France but their colonies also. The Russian patent extends to all of the Russian possessions.

"The disbursements for filing an application in the Australian states, namely, Queensland, Victoria, New South Wales, South Australia, Western Australia and Tasmania are $5.00 on filing the application, $10.00 on allowance of same, and $25.00 for preparation of the sealing of patent; New Zealand, $20.00; Mexico, $75.00; Natal, $50.00; Japan, $75.00; Jamaica, $150.00."

This talk on patents was quite interesting to Fred, and very instructive to George, and they thanked their father for it.

Photographs by C. M. D'EnvilleA Sun Dial Made of ConcreteAn excellent illustration of the possibility which concrete offers in ornamental as well as practical construction. This sun dial, complete, cost approximately ten dollars, and may be duplicated by any clever boy. See formula for concrete onpage 20.

Photographs by C. M. D'Enville

A Sun Dial Made of ConcreteAn excellent illustration of the possibility which concrete offers in ornamental as well as practical construction. This sun dial, complete, cost approximately ten dollars, and may be duplicated by any clever boy. See formula for concrete onpage 20.

"Boys," he said to them next morning, "why not try your hands on a sundial? You will find iteasy to make, and if properly set up it will keep accurate time. There is a nice place for one near the bridge on the new grounds, as there is a stump there, the top of which can be cut off smooth, and it stands out full in the sun.

Fig. 64. Sundial

"Go to our jeweller in the city and get him to give you an old tin clock-dial, like the one shown inFig. 64. If you cannot get one, make a dial out of cardboard yourself, printing the hours in ink. Slit the dial from the centre to a point directly underneath the number 12, if you have Arabic numerals on your dial.

"Then cut out a triangular blade or gnomon, like the one shown. If your dial is of tin, make the blade of tin, or cardboard if your dial is of cardboard.

"Insert the blade in the slit of the dial and secure it to the top of the stand you have selected—with tacks if your dial is cardboard, with small nails if it is tin. Then your sundial will be completed and ready for business.

"At 12 o'clock, there will be only the shadowof the thin edge of the blade over the dial, but as the sun moves, so will the shadow, so as to tell always the correct time of day. You will find this not only a useful but a quaint and artistic addition to the grounds, and not at all expensive."

"Papa," said George, "mamma wants a flower bed made in the front garden, and she would like to have it an oval or elliptical shape. I have promised to make it for her, but I do not know how to make the shape, and I wish you would tell me."

"Certainly, my boy, I will show you. It can be done easily with a string and two wooden pegs. Follow the lines I make on the blackboard. First we must decide on the length and width of the oval or rather ellipse required. Then draw two straight lines, A B and C D,Fig. 65, equal to the two axes, and bisect or halve each at right angles. Set off from C half the length of the great axis at E and F, which are the twofociof the ellipse. Take an endless string, as long as the three sides of the triangle, C E F, fix two pins or nails in the two foci, one at E and one at F. Lay the string around E and F, stretch it with a marker G, and it then will describe the desired ellipse.

Fig. 65. Drawing an ellipse

"This is not at all difficult, and will answer forany kind of an ellipse, short or long, narrow or wide. This is called the "gardener's method." The main thing is to get the two points, E and F. This distance is always half of the long diameter A B, no matter what that may be, and this distance is then transferred by taking C as the starting point, measuring from there until the other point of measurement cuts the long diameter, as at E and F.

"The ellipse has many peculiar and useful qualities, which you will doubtless discover before long."

Now, papa!" said Jessie the following evening, after Mr. Gregg and the family had strolled down to the river bank to enjoy the cool air, "you promised to tell me about the tides and the moon—when you could spare time. Haven't you got time now?"

"I may as well say all I intended now, my dear, and leave some other matters for future consideration. As this subject may tax your patience, I hope you, Fred, and George, will give me your earnest attention.

"In order to have a clear understanding of the movements of the tides and their supposed causes, you must know something of the moon's influence over them; as this knowledge will aid you very much in remembering what I am about to say.

"The earth is a globular body. One reason for this belief, among many others, is that sailors or others who go to sea soon observe that as they sail from shore, the lower portions of mountains, steeplesor other high objects, are gradually lost sight of while the higher parts do not so soon disappear. Persons on shore first notice the upper portions of masts, and the smoke-stacks of approaching vessels, which would not be the case, if the earth were a plane, but is very easily accounted for, on the supposition of its being a sphere, as you can readily understand by looking atFig. 66. Several navigators have sailed completely round the earth by continuing in the same direction, and coming at last to the same place from which they started. The earth, however, is not a perfect sphere but a spheroid like an orange; having its equatorial longer than its polar diameter or axis. It is flattened at the poles, and more protuberant at the equator. The diameter at the equator is 7,977 miles, and at the poles 7,940, a difference of 37 miles.

Fig. 66. Proof of earth's rotundity

"You know that the cause of day and night is the rotation of the earth on its own axis. It shows a large portion of its surface to the sun continually, or in other words, the sun is always shining on someportion of the earth's surface. You are also aware of the earth and its satellite, the moon, both being held in their orbits by the sun's attraction, the moon being further kept in her orbit by the attraction of the earth. Now the earth is composed of three main elements, air, water, and land, and if you consider, for a moment, that the daily rotatory movement of the earth is something like 1,000 miles an hour, this rapid speeding through space must have some effect on air and water in assisting or retarding their flow.

Fig. 67. Phases of the moon

"Nature has divided time, and man has named and subdivided it into years, months, and days. The natural month, however, does not consist of four weeks, nor is the natural year made up of the twelve calendar months given us by the almanac. A natural, or lunar, month is the time the moon takes to perform her journey round the earth, which is 27 days 7 hours, and 43 minutes; this is called the periodical month, while the average calendar or synodical month consists of 29 days 12 hours and 44 minutes. The light of the moon is borrowed from the sun, for if it were her own light, she would shine all the time and not be subject to her present phases. The moon is seen by means of the light which comes to it from the sun being reflected fromit. Its changes, or phases, depend upon its relative position to the earth and the sun. When the moon is in opposition to the sun at A (Fig. 67) the lighted side is turned toward the earth, as A, and it appears full. When the moon is in conjunction at E with the sun, its dark side is turned toward us, and it is invisible, as ate. As it proceeds in its orbit, as at F, a small part of the light side is seen, and then we have what is called a new moon; and we continue to see more and more of the light side, as the moon approaches at G and H, to the state of opposition or full moon. The waning or decreasing of the moon takes place in the same manner, but in a contrary order. The earth must perform the same office to the moon that the moon does to us; and it will appear to the inhabitants of the moon (if there be any), like a very magnificent moon, being to them about thirteen times as large as the moon is to us and it will also havethe same changes or phases. Hence it is evident, that one half of the moon is never in darkness, the earth constantly affording it a strong light, during the absence of the sun; but the other half has a fortnight's light and darkness by turns.

"The moon's orbit is elliptical, and she also rotates on her axis and takes the same time to circle the earth, consequently every part of the moon is successively presented to the sun, yet the same hemisphere is always turned to the earth. This has been discovered by observation with good telescopes. The length of a day and night in the moon is more than twenty-nine and a half days of ours; and while her year is the same length as ours, being measured by her journey around the sun with us, so she has but twelve days and a third in a year. Another remarkable circumstance is that the moon's hemisphere next the earth is never in darkness, for when it is turned from the sun, it is illuminated by light reflected from the earth in the same manner as we are lighted by a full moon. The other hemisphere of the moon however, has a fortnight's light and darkness by turns. If there are inhabitants in the moon, which is doubtful, the satellite will appear to them to be about thirteen times as large as the moon does to us, and when it isnew moon to the earth, it is full earth to the moon.

"There are many things regarding our relationship to the moon that would be of interest, if I had time to explain them, such as eclipses, the moon's surface as seen through telescopes, its supposed influence on the weather, etc., but I fear too much moon might prove tiresome. Beside I have shown you sufficient to enable you to understand the relationship existing between the moon and the tides, generally accepted as the true theory.

"If we agree that the tides are occasioned by the attraction of sun and moon, more particularly the latter, we can readily understand their dependence on some known and determinate laws. Our almanacs published long in advance give the exact time of high water at any prominent port in the United States on the morning and afternoon for every day in the year; and seafaring men can tell you when the tide will be high or low, notwithstanding the fact that these movements are not fixed. They know from experience that the time of ebb and flow varies about three quarters of an hour each day.

"The first person who clearly pointed out the accepted cause of the tides and showed its agreementwith the effects, was Sir Isaac Newton. He discovered a relationship between the moon and the tides, and by the application of his new principles of geometry, the attraction was made clear.

"The ocean, it is well known, covers more than one half the globe; and this large body of water is found to be in continual motion, ebbing and flowing alternately, without the least intermission. For instance, if the tide is now at high water mark, in any port or harbour which lies open to the ocean, it will presently subside, and flow regularly back for about six hours, when it will be found at low water mark. After this it will again gradually advance for six hours; and then recede in the same time to its former situation, rising and falling alternately twice a day, or in the space of about twenty-four hours. The interval between its ebb and flow is not precisely six hours, for there is a little difference in each tide; so that the time of high water does not always happen at the same hour, but is about three quarters of an hour later each day, for about thirty days, when it again recurs as before. For example, it is high water to-day at noon, it will be low water at eleven minutes after six in the evening; and, consequently, after two changes more, the time of high water the next day will beat about three quarters of an hour after noon; the day following it will be at about half an hour after one, the day following that at a quarter past two, and so on for thirty days; when it will again be found to be high water at noon, as on the day the observation was first made. This exactly answers to the motion of the moon which rises every day about three quarters of an hour later than upon the preceding one, and by moving in this manner round the earth, completes her revolution in about thirty days, and then begins to rise again at the same time as before.

"To make the matter still plainer; suppose, at a certain place, it is high water at three o'clock in the afternoon, upon the day of the new moon; the following day it will be high water at three quarters of an hour after three; the day after that at half an hour past four; and so on till the next new moon, when it will again be high water exactly at three o'clock, as before. By observing the tides continually at the same place, they will always be found to follow the same rule; the time of high water, upon the day of every new moon, being exactly at the same hour, and three-quarters of an hour later every succeeding day.

"The change of the tides is in such exact conformitywith the motion of the moon that, independently of mathematical calculations, a thoughtful person would certainly be induced to look to her as their cause.

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