DIE KONSTRUKTION und ANLEGUNG DER BLITZABLEITER zum Schutze aller Arten VON GEBÄUDEN SEESCHIFFEN und TELEGRAFEN STATIONEN.Von Dr. Otto Buchner.Weimar. 1867. 8vo.

(Abstracted by Alexander Siemens).

The serious damage caused in Schleswig-Holstein by lightning led to an official inquiry into the subject, the following is an abstract of the first report of the commission.

It is stated that trees, by their gradual but uninterrupted discharge of electricity, have a dispersing effect upon thunder-clouds, and tend to lessen the energy of lightning. In six cases out of the twelve examined, houses with trees close by, were struck, but not so heavily as in another case where the building had no protection whatever. Trees do not, however, afford complete protection to neighbouring buildings, their conductive capacities not being sufficient to convey, in the immeasurably short time required, such heavy discharges of electricity as lightning flashes. This is instanced by their being often wholly, or partially, destroyed by the current, or, as occurred in four cases, by their passing it over to better conductors, buildings, &c.

If a thunder-cloud passed over a perfectly plane surface, the discharge would take place in a vertical line between earth and cloud, but prominent objects, such as isolated trees, buildings, lightning conductors, and iron pumps, reaching down to underground water, act as attractive points, and divert the discharge, the path of which is also influenced by any conductors which happen to come between them and the thunder-cloud, such influence depending upon the capacity of the conductors. So that, generally an electric discharge chooses that path which, taking the distance into account, offers the best means of conduction.

It is frequently found that inflammable material is struck by lightning without being ignited, on account, it is presumed, of the short duration of discharge not allowing the material to become sufficiently hot to burn, but whether the duration of discharge is dependent upon the nature of the charge of the thunder-cloud, or solely upon the condition of the objects struck, has not been ascertained. The latter is, however, not without influence, as in two of the four cases which resulted in fire, the cause was presumably due to newly gathered hay stored at the top of the houses struck, and in the other two cases to trees, which were struck at the same time, the hay and the trees being bad conductors, and prolonging the duration of discharge.

Four cases are given of buildings having lightning conductors being struck.

The first case is that of a windmill, the conductor of which terminated in a sheet of metal placed in a well near the building. The discharge was exceedingly heavy, but beyond the platinum point being almost entirely fused, no other damage was done.

The second is that of a house with two separate lightning conductors, each ending in a copper plate, spirally coiled up, and laid in underground water. One of the conductors was struck, and the lightning passed from it, and, running horizontally along the thatched roof of the house, descended by the other, causing no damage.

The third case refers to a church and, adjoining it, a school building. A portion of the discharge was diverted from the conductor by an anchor in the church wall three metres off (which it magnetized), and forced its way through the ceiling of the school-house to a number of gas brackets, which were turned up towards the ceiling. It was ascertained that the ground floor of the house was completely under water, and well connected to earth through the gas mains and an iron pump, a good continuous conductor thus being formed.

Accordingly, the report recommends that lightning conductors should be connected to the large masses of metal, such as gas and water mains, which are found in our houses.

In the fourth instance a church had a lightning conductor, which was connected to the top of two large iron supports running through the steeple to the nave, and which terminated in a coiled earth-plate, 1 sq. metre (11 sq. ft.), supposed to lie in water 7 metres (23 ft.) underground. The lightning struck the conductor and, passing to the iron supports, sprang from one through the outer wall, close to an iron window frame, and from the other across the stucco ceiling, going to earth 100 feet off through the altar gilding, which it blackened. It was subsequently found that the copper earth-plate was only ⅓ metre (1 ft. 1 in. sq.), and that it was buried loosely round the rod in dry sand, the rod itself reaching 2 to 3 metres further down, and just touching water without an earth-plate, and also that the two supports had no earth connection, thus forming a great danger instead of a safeguard to the church.

(Abstracted by R. Van der Broek.)

The book is divided into two parts:

1. General, or Introductory, and

2. Practical.

The first, or Introductory part, is sub-divided into:

1. Historical and statistical notes;

2. The theory of atmospheric electricity, and of the lightning conductor; and

3. A chapter on natural lightning conductors.

The great philosopher, Lichtenberg, of Gottingen, said in the year 1794: “People are struck and their dwellings are destroyed by lightning because they will have it so. It does not matter to us whether parsimony, carelessness, ignorance, or anything else is the cause of this.” The author asserts that this dictum may be equally applied to the present generation.

Professor J. H. Winkler, of Leipzig, discovered, in the year 1746, that electricity is the principal cause of thunderstorms.

The first lightning conductor in Germany was erected 1769, at Hamburg, on the steeple of the Jacobi Church.

Between the years 1835 and 1863, a period of 19 years, 2238 persons werekilledby lightning in France. The maximum in one year (1835) was 111 and the minimum 48. The total number of personsstruckby lightning amounted to 6714; of this large number 1700 persons would have escaped, if they had been careful to avoid the neighbourhood of trees, whilst the storms were raging. The greatest number of the accidents caused by lightning occur during the months of July and August; not a single fatal case is on record for the months of November, December, January, and February. The annual average number of persons killed by lightning was 3 in Belgium, 22 in England, and 10 in Sweden. In the low-lying Departments of France the average is 2 or 3; the average increases rapidly for the Mountainous Departments to 24, 28, 38, 44, and (in Auvergne) 48. The per centage of males in France is 67, females 10, and in the remaining cases the sex was not stated. In Prussia the proportion is 184 males to 105 females, in Sweden 5 males to 3 females.

The largest number of persons killed byonedischarge is 8 or 9.

The author states that the return shock is only mechanical in its effects.

Professor Müller lays down the following conditions for lightning conductors:—

1. The rod must end in a very sharp point.

2. There must be no want of continuity between the extreme point and the earth contact: and

3. The different parts of the conductor must be of the requisite dimensions.

In practice we find that the first mentioned condition is incorrect, as sharp points are too liable to be fused.

The rod must be made of a pyramidal or a conical form. Short rods of not above 2 metres (6 feet 7 inches) in length may be made of a cylindrical form. The best form of rod is one tapering from a base of from 50 to 60 millimetres (2 inches to 2·4 inches) in diameter to a diameter of not less than 14 millimetres (0·56 inches). As it is difficult to fix rods of a height of 10 metres (33 feet), it is better to erect one long rod, and several shorter ones on different parts of the roof and connect them together. The principal rod should have aheight of from 2½ to 3 metres (8 to 10 feet) and the secondary rods (Nebenstangen) should be at least 1 metre (3 feet 3 inches) high.

The form of point universally used in Germany is a strongly firegilded copper cone.

Kuhn advocates the use of chemically pure silver for the points. His arguments in favour of this metal are incontrovertible. The conducting power of silver is 1·36; that of pure copper being 1. The fusibility of silver (1,000 c.) is sufficiently high for the purpose. The atmosphere, unless it contains sulphur in a gaseous or a liquid form, has no effect on silver. Silver is cheaper than platinum, and not more expensive than a gilded copper cone, and it can be easily soldered to other metals.

The point should be screwed on, as well as soldered to the rod. All other but the conical form of point should be rejected.

The best material for the earth contact is galvanised iron.

As regards the protection of sea-going vessels, Snow Harris’s arrangement, converting, as it were, the vessel into one mass of metal, is perfect.

The first practicable lightning conductor for the protection of telegraph wires was constructed by Steinheil in 1846. His arrangement was somewhat modified by Breguet and Fardely. Meiszner introduced a real improvement.

On the Prussian railway telegraphs two “point-systems” are in use, one for small stations, and the other for larger stations.

It is desirable that all lightning conductors be examined once a year. The metallic connection throughout must be perfect, the point must be kept free from rust, and the earth contact must be good. The whole circuit should also be tested by means of a battery and a galvanometer.

(Journal of the Society of Telegraph Engineers, May 12, 1875.)

(Abstracted by W. H. Preece, C.E.)

Arguing from the case of a powder magazine at East London, Cape of Good Hope, when the iron conductor was led into a cemented water-tank, frequently dry, and where it was destroyed, the author raises two questions:

1. Should such tanks be used for earth?

2. Is iron the proper metal to use?

He gives a decided negative reply to the first, and advocates the use of galvanized iron properly protected from atmospheric action. He suggests rods 1 inch in diameter, or bands 2in. × ⅜in. thick.

In the discussion which followed it was mentioned that the ground about Torquay is so insulated that plates had to be carried out to sea to secure a good earth for the telegraph there, and that of the numerous churches which had been inspected, there was not a single conductor that could be passed. It was pointed out that when copper conductors were fixed with iron wall-eyes—a frequent thing—galvaniccurrents were set up, and the conductor destroyed at the ground line.

It was stated that the earth connection of a supposed perfect conductor was found to be equal to a resistance of 1,000 Ohms.

Mr. Preece, Major Malcolm, R.E., Dr. Mann, Mr. Pidgeon, Mr. Kempe, Mr. Graves, Mr. Spagnoletti, and Mr. Latimer Clark, took part in the discussion.

(Abstracted by G. J. Symons, F.R.S.)

States that there are certain principles accepted as established facts,e.g., that conductors should be of metal of high conductivity, and of adequate dimensions. That in 1854 the French electricians held that a “quadrangular iron bar ¾ in. diameter, was sufficient in conducting power for all purposes.” Since then, wire ropes, owing to their pliability, have nearly superseded solid rods, and copper has been preferred to iron because of its higher conducting power and less liability to oxidise. But provided that the iron be galvanized, and of five times the sectional area of a copper conductor, considers the metal immaterial.

Author states that the resistance of a conductor increases with its length, therefore sectional area of conductor must be increased for lofty buildings. Modern French electricians employ copper rope 0·4 to 0·8 in. diameter. M. R. Francisque Michel considers galvanized iron wire rope 0·8 in. diameter sufficient for all ordinary cases. Copper wire rope 0·5 in. diameter (6¾ oz. per foot) recently applied to St. Paul’s Cathedral.

Importance of perfect earth connection strongly insisted upon, but it is matter of some difficulty, and the oxidation of the earth terminals, and their inefficiency doubtless lead to most of the reported failures of lightning conductors. Author quotes Pouillet and Becquerel, as saying, that for the efficient discharge of the lightning, which could be carried by a copper rod 0·8 in. diameter, contact must be obtained with 1,200 square yards of moist earth, but this large requirement can only easily be obtained in towns by connection with the water mains. Various modes of obtaining adequate earth contact by iron harrows, Callaud’s grapnel in basket of coke, &c., described.

Explains the rationale of testing goodness of earth currents by the galvanometer. Calls attention to the destruction of upper terminals of conductors to factory chimneys by the emission of sulphurous fumes, and suggests that they might be cased in lead.

Calls attention to the importance of every joint being made absolutely perfect.

Urges the superiority of points for upper terminals, owing to their facilitating silent discharge, and rendering lateral discharges from the conductor less probable.

Thinks that multiple points of copper kept fairly sharp and clean are, on the whole, the best upper terminals.

Considers that all large masses of metal in a building should be connected with the conductor; but quotes M. Callaud, who holds the opposite view. Dr. Mann, however, points out that if the conductor be efficient and perfect, the accidents which M. Callaud contemplates, and on which he bases his arguments, could not occur.

Calls attention to the ready path afforded by the column of heated smoke discharged by chimneys, and hence alludes to the placing of a coronal conductor, as well as a multiple point on important chimneys.

Suggests the utilization of rain water pipes, by perfecting their joints, and securing a good earth connection at their base.

(Abstracted by W. H. Preece, C.E.)

A carefully prepared theoretical and practical paper, adapted for use in India. Author advocates the use of iron from its higher temperature of fusion, and greater specific heat than copper, its long protection from decay by galvanization and its cheapness. He prefers wire cables from the absence of joints in them. He gives precise instructions for the formation of a good earth, and advocates periodic electrical tests.

(Abstracted by W. H. Preece, C.E.)

The authors controvert Clark Maxwell’s views that a building would be perfectly protected from lightning by being enclosed in a network, or cage of wires, without the use of the earth. They object to the application of the laws of static electricity alone to such a case. Current induction intervenes, and this is not subject to the screening action of a cage. Hence, though a metallic cage may assist the protection of a house, it does not do so perfectly.

(Abstracted by G. J. Symons, F.R.S.)

Author states that ever since lightning conductors have been used, there have been disputes as to whether the discharge passes over the surface of conductors or through their mass. Snow Harris, Henry, Melsens, and Guillemin have held that it passed over the surface; Faraday held the opposite view.

The arguments in favour of the surface form are, in the opinion of the author, deductions from exploded theories, from imperfect experiments, or from erroneous interpretations of well ascertained facts.No direct experiments have ever been made to solve the question, as far as the author knows. Quantities of electricity, that is static discharges from condensers, are in incessant use for telegraphic purposes, and are found to follow exactly Ohm’s laws, even with the most delicate apparatus. The knowledge of the flow of electricity through conductors, of the retarding influence of electrostatic capacity upon this flow, and of the distribution of charge, has become so much greater of late years through the great extension of submarine telegraphy and the labours of Sir William Thomson, Clerk Maxwell, and others, that the author questions if any English electrician would now be found to argue in favour of the surface form. Nevertheless, as ribbons and tubes still continue to be used, and it appeared very desirable to settle the question experimentally, the author determined to try and do so.

Dr. Warren de la Rue, who is always ready to place his splendidly equipped laboratory at the service of science, not only allowed the author to use his enormous battery and his various appliances, but aided him by his advice, and assisted him in conducting the experiments.

Copper conductors, 30 feet long, of precisely the same mass, (a) drawn into a solid cylinder, (b) made into a thin tube, and (c) rolled into a thin ribbon, were first of all obtained. The source of electricity was 3,240 chloride of silver cells. The charge was accumulated in a condenser of a capacity of 42·8 microfarads. It was discharged through platinum wire of ·0125 diameter, of different lengths. The sudden discharge of such a large quantity of electricity as that contained by 42·8 mf. raised to a potential of 3,317[5]volts is very difficult to measure. It partakes very much of the character of lightning. In fact, the difference of potential per unit length of air is probably greater than that of ordinary lightning itself. It completely deflagrates 2½ inches of the platinum wire, but by increasing the length of the wire it could be made to reproduce all the different phases of heat which are indicated by the various shades of red until we reach white heat, fusion, and deflagration. Hence the character of the deflagration, which is (by its scattered particles) faithfully recorded on a white card to which the wire is attached, is a fairly approximate measure of the charge that has passed, while the length of wire, raised to a dull red heat, is a better one, for any variation in the strength of the current within moderate limits is faithfully recorded by the change of colour.

5. The electromotive force of the chloride of the silver cell is 1·03 volt.

Experiment 1.—Similar charges were passed through the ribbon, tube, and wire, and in each case 2½ inches of wire were deflagrated. No difference whatever could be detected in the character of the deflagration.

Experiment 2.—Ten inches of wire were taken and similar charges passed through. In each case the wire was raised to very bright redness, bordering on the fusing point, and in two cases the wire broke. In each case the wire knuckled up into wrinkles, and gaveevidence of powerful mechanical disturbance. The same wire was not used a second time. No difference could be detected in the effect through the different conductors.

Experiment 3.—Silver wire of the same diameter and length was used, and similar charges transmitted through it. Redness was barely visible, but the behaviour of the wire was similar in each case.

The conclusion arrived at unhesitatingly was, that change of form produced no difference whatever in the character of the discharge, and that it depended simply on mass.

As it might be urged that the length of conductor tested was so short, and its resistance so small that considerable variations might occur and yet be invisible, similar lengths (30 feet) of lead—a very bad conductor, its resistance being twelve times that of copper—were obtained, drawn as a wire, made as a tube, and rolled as a ribbon, each being of similar weight.

Experiment 4.—Charges from the same condenser, 42·8 mf., but with 3,280 cells, were passed through, and the discharges observed on 6 inches of platinum wire 0·0125 inch diameter, which in each case was heated to bright redness. No variation whatever could be detected, whether the wire, the tube, or the ribbon were used.

Experiment 5.—In order to form some idea as to how closely any variation in the character of the discharge could be estimated, a long piece of platinum wire was used, and the length adjusted until just visible redness was obtained; then a diminution of 10 per cent. (3 feet) produced a marked change to dull redness, and further excisions raised the temperature to brighter and still brighter red.

The conclusion arrived at was that any change in resistance of 5 per cent. would have been clearly and easily discernible.

It therefore appears proved that the discharges of electricity of high potentials obey the laws of Ohm, and are not affected by change of form. Hence, extent of surface does not favour lightning discharges. No more efficient lightning conductor than a cylindrical rod or a wire rope can therefore be devised.

(Abstracted by G. J. Symons, F.R.S.)

This author gives a formula for determining the area protected, which he considers to vary with the height of the storm cloud, and the elevation of the ground. He states that the mean elevation of the storm clouds at Constantinople is as low as about 325 feet. He says that conductors placed near the extremities of a building have their radius of protection diminished, and therefore recommends a line conductor running round the building. (Thecircuit des faitesof the Paris Municipal Commission, see ante page68).

He says that his formula leads to nearly the same results as have hitherto been adopted, but he gives three examples, the results of which are—length of conductor being 1·00, radius protected is respectively 3·80, 1·10, and 2·20.

ON THE SPACE PROTECTED BY A LIGHTNING CONDUCTOR. ByW. H. Preece, C.E. (Phil. Mag., Dec., 1880.)

(Abstracted by G. J. Symons, F.R.S.)

In the early part of this paper the author discusses the distribution of electricity in the space between the storm cloud and the earth’s surface, and points out that the air in an electric field is in a state of tension or strain; and this strain increases along the lines of force with the electromotive force producing it until a limit is reached, when a rent or split occurs in the air along the line of least resistance—which is disruptive discharge, or lightning.

Since the resistance which the air or any other dielectric opposes to this breaking strain is thus limited, there must be a certain rate of fall of potential per unit length which corresponds to this resistance. It follows, therefore, that the number of equipotential surfaces per unit length can represent this limit, or rather the stress which leads to disruptive discharge. Hence we can represent this limit by a length. We can produce disruptive discharge either by approaching the electrified surfaces producing the electric field near to each other, or by increasing the quantity of electricity present upon them; for in each case we should increase the electromotive force and close up, as it were, the equipotential surfaces beyond the limit of resistance. Of course this limit of resistance varies with every dielectric; but we are now dealing only with air at ordinary pressures. It appears from the experiments of Drs. Warren de la Rue and Hugo Müller that the electromotive force determining disruptive discharge in air is about 40,000 volts per centimetre, except for very thin layers of air.

If we take into consideration a flat portion of the earth’s surface, and assume a highly charged thunder-cloud floating at some finite distance above it, they would, together with the air, form an electrified system. There would be an electric field; and if we take a small portion of this system, it would be uniform.

If the cloud gradually approached the earth’s surface, the field would become more intense, the equipotential surfaces would gradually close up, the tension of the air would increase until at last the limit of resistance of the air would be reached; disruptive discharge would take place, with its attendant thunder and lightning.

Fig. 1.

If the earth-surface be not flat but have a hill or a building, as A or B, upon it, then the lines of force and equipotential planes will be distorted, as shown in fig. 1. If the hill or building be so high as to make the distance HD equal to the limit of resistance (fig. 2), then we shall again have disruptive discharge.

Fig. 2.

If instead of a hill or building we erect a solid rod of metal, G H, then the field will be distorted as shown in fig. 2. Now it is quite evident that whatever be the relative distance of the cloud and earth, or whatever be the motion of the cloud, there must be a spaced d´along which the lines of force must be longer thanc c´or H D; and hence there must be a circle described around G as a centre which is less subject to disruptive discharge than the space outside the circle; and hence this area may be said to be protected by the rod G H. The same reasoning applies to each equipotential plane; and as each circle diminishes in radius as we ascend, it follows that the rod virtually protects a cone of space whose height is the rod, and whose base is the circle described by the radius Gc. It is important to find out what this radius is.

Fig. 3.

Let us assume that a thunder-cloud is approaching the rod A B (fig. 3) from above, and that it has reached a point D´ where the distance D´ B is equal to the perpendicular height D´ C´. It is evident that if the potential at D´ be increased until the striking-distance be attained, the line of discharge will be along D´ C´ or D´ B, and that the length A C´ is under protection. Now the nearer the point D´ is to D the shorter will be the length A C´ under protection; but the minimum length will be A C, since the cloud would never descend lower than the perpendicular distance D C.

Supposing, however, that the cloud had actually descended to D when the discharge took place. Then the latter would strike to the nearest point; and any point within the circumference of the portion of the circle B C (whose radius is D B) would be at a less distance from D than either the point B or the point C.

“Hence a lightning-rod protects a conic space whose height is the length of the rod, whose base is a circle having its radius equal to the height of the rod, and whose side is the quadrant of a circle whose radius is equal to the height of the rod.”

Upon this rule the author makes the following concluding remarks:

“I have carefully examined every record of accident that I could examine, and I have not yet found one case where damage was inflicted inside this cone when the building was properly protected. There are many cases where the pinnacles of the same turret of a church have been struck where one has had a rod attached to it; but it is clear that the other pinnacles were outside the cone; and therefore, for protection, each pinnacle should have had its own rod. It is evident also that every prominent point of a building should have its rod, and that the higher the rod the greater is the space protected.”

(Abstracted by R. Van der Broek.)

On the date mentioned, between three and four o’clock in the afternoon, a violent storm burst over Antwerp, during which the lightning struck the Railway Terminus, without, however, occasioning any other damage than the perforation of a single hole in one of the glass squares of the roof.

The author states that the effect of the discharge on this square of glass, which was about 4mm(0·2in.) thick, was remarkable; it appeared as if it had been traversed by a projectile from below, the perforation, viewed from above, being broken and chipped, whilst viewed from below it showed a clean edge. The sinuosities caused by the chipping on the upper surface had rounded edges, and the glass appeared to have been subjected to incipient fusion. Not a single fragment of glass was found on the glass squares or in the gutters of the roof.

The author arrives at the following conclusions: The square of glass was pierced in the same manner as any square of similar nature and dimensions, placed in identical circumstances, would be, were ittraversed by a spherical projectile fired at a low velocity from a firearm. The fracture resembled one that would be produced by a missile thrown from below, that is to say, from the earth to the sky.

The form of the opening indicated that the earth was positively electrified.

The author notices that, according to M. F. Duprez, negative electricity generally shows itself in abnormal conditions of the atmosphere, during storms, rains, &c., and when the wind blows from the western quarters between N. and S. Now, on the day in question, it rained and the wind blew from the west.

The author publicly thanks M. Ruhmkorff for his skilful and disinterested co-operation in proving the correctness of his (the author’s) view of the distribution of the electricity at the Antwerp discharge. M. Ruhmkorff has, at request, pierced squares of ordinary glass about 1mm(0·04in.) thick by the discharge of his great induction apparatus charged by a powerful Leyden battery.

(Abstracted by R. Van der Broek.)

As the author states in his preliminary observations that it is impossible to give a complete condensed description of the Lightning Protector, which he erected on the Town Hall at Brussels, we will merely draw attention to a number of facts, regarding the system followed, some of them, we believe, of a novel description.

M. Daniel Colladon, the author states, has observed that as a rule lightning does not strike a single part or prominent point of the objects that are struck or destroyed by it; and that, in the majority of cases, it does not strike in the form of a single spark, but in the form of a sheet with one or more principal centres of intensity. The correctness of this observation, the author considers fully borne out by the ravages which the electric discharge committed on the Town Hall at Brussels, on the 10th September, 1863. He gives an elaborate description of the effects of the flash on the building. It is interesting to note that the ravages principally took place at the side exposed to the west north-west wind, which was blowing at the time the building was struck.

In the ensuing winter the Municipal Council of Brussels took into consideration the necessity of protecting the Town Hall against a similar disaster, and the author was requested to superintend the erection of lightning protectors on the building.

The characteristics of the author’s system, as exemplified by the lightning protectors erected on the Brussels Town Hall, may be briefly summarised as follows:—

1. The points are very numerous—of three kinds; some long, sharp, and gilded, others of middling length, made of iron;and finally some small and very sharp, consisting of copper.

2. The points are replaced byaigrettes(brushes of points diverging from a common base).

3. The conductor is not insulated.

4. The connections are simple and unchangeable, the joints are each embedded in a mass of zinc.

5. The surface exposed to the air is considerable.

6. The conductor consists of thin, and numerous wires, which are very flexible, so as easily to be led round all the corners of the buildings.

7. The conductor is made of galvanised iron.

8. The earth connections are multiple: firstly, a well within which a large surface of metal is plunged; and, secondly, two enormous networks of metal pipes, offering an immense contact surface with the earth. One of these networks is in direct communication with all the reservoirs and all the water sources of the environs of Brussels and also in indirect communication with two rivers and two canals.

The author has arrived at the conclusion that the height of the rod is a secondary question, as the radius of protection has not been determined by irrefutable proofs, and as that length is, in comparison with the distance and the extent of the thunder-clouds, so small a factor that it may safely be neglected. The author states that he has been greatly gratified to meet with the same opinion in a paper which Mr. W. H. Preece published in Vol. I., No. 3, page 366, of the Journal of the Society of Telegraph Engineers for 1872: “When we consider the distance of the cloud and the area of its surface, the height of a building vanishes in the general figure.”

The author points out that M. Perrot has endeavoured to demonstrate by experiment that the neutralizing area of a lightning protector surmounted by a crown of sharp points is far more extensive than that of an ordinary protector. M Perrott further thought, and MM. Babinet and Gavarret shared his opinion, that it is sufficient to shelter the ordinary protector from discharges of lightning by arming it with numerous, long, sharp, and well conducting divergent points. M. Gavarret after having repeated Mr. Perrott’s experiments, found the results so conclusive that he wrote to the author in the beginning of 1865: “It is at the present time no longer permitted to erect lightning protectors with single points.”

The metal of which the points are made must be a very good conductor. With regard to their conductivity, the metals follow each other in the following order: copper, silver, iron, platinum. No metals are used but those which resist fusion. The author rejected platinum and silver: the former because it fuses very readily by the electric discharge; and the latter, because it has, in his opinion, no advantage over copper.

The conductor, although galvanized, received several coats of paint; but the points (aigrettes) of course remained metallic. With regard to the general principle of connecting the protector with any masses of metal which may be about the building, the author has ever since1865 endeavoured to demonstrate, that it is not sufficient, as might at first sight be supposed, to form that connection at one single point; there must be at least two points of contact, so as always to ensure a closed metallic circuit.

The contact with the water presents a surface of about ten square metres (12 sq. yds.), bringing both surfaces of the cylinder into account.

With regard to the earth connection, the author quotes M. Perrot, who remarks that with the ordinary protector the surface immerged offers a resistance at least 10,000 times greater than the conductor itself; it is therefore necessary to increase the surface of the earth-plate as much as possible.

In order to retard as much as possible the oxidation of the cylinder, the author introduced two hectolitres (6 bushels) of lime into the well, thus rendering the water alkaline.

(Abstracted by R. Van der Broek.)

In this pamphlet the author describes in § 1 an apparatus to show the presence of atmospheric electricity in telegraph wires.

In §§ 2 and 4 he explains how the apparatus is joined up in the Belgian telegraph offices.

§ 3 contains a résumé of observations made at the government telegraph offices between June, 1875, and March, 1876.

The author states in this paragraph that, on the 19th of June, 1875, the Rheo-Electrometer at the office at Louvain, showed a deflection of 85° East, although there was not the slighest appearance of atmospheric electricity. The fact was, that at the time a thunder storm was raging at Beverloo, distant from Louvain about 40 kilometres (25 miles).

(Abstracted by R. Van der Broek.)

On the 3rd of July, 1874, the church of Ste. Croix, at Ixelles, was struck by lightning. The building was provided with a lightning protector, which was constructed as follows: The point consisted of a platinum cone of about 30° (the form officially adopted in France in 1855), all the supports of the protector were soldered with zinc. This was attached to the steeple, and rose to 53 metres or 174 feet above the pavement. It consisted of an iron rod 18 mm. (0·71 in.) in diameter (M. E. Sacré’s system). The conductor passed from the principal roof along the roofs, descending to a point near a pump, behind the vestry, where the well (W) was situate. There is an abundance of water in the well, which is about 7 m. (23 ft.) deep. The conductor terminated in the well, by a cast-iron plate 0·65 m. (2 ft. 1 in.) by 0·50 m. (1ft. 8 in.), thus presenting a surface of 0·654 ⬜ m. (7 sq. ft.). A little in front of the transept there is a supplementary rod B 5·25 m. (17 ft. 3 in.) high, 11 m. (36 ft.) distant fromthe point (c in diagram) which was struck; and 22 m. (72 ft.) distant from that point there was a second rod D, whose height was 9 m. (29½ ft.) above the top of the roof.

The damage to the church was trifling, but the author contends that the fact of the church having been struck at all, proves that a building armed with a protector constructed on the usual principle is not completely protected.

Plan and Elevation of Church of Ste. Croix, at Ixelles

(Abstracted by R. Van der Broek.)

This treats § 1 of observations on the distribution of the spark of electric batteries and machines over numerous metallic conductors of different sections, lengths, and nature, and on the passage of electricity of tension in bad conductors.

§ 2. Effects of soldered joints on the conductivity and the resistance of conductors. Interrupted lightning protectors.

§ 3. The distribution of sparks from Holtz’s machine and Ruhmkorff’s coil over two conductors outwardly identical, but one of iron and the other of copper. Comparative resistance to fusion and rupture for iron and copper conductors. Identical damage produced by discharges in several homogeneous and solid conductors.

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