A PRACTICAL TREATISE ON LIGHTNING CONDUCTORS.By Henry W. Spang.Philadelphia. 1877.

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

This pamphlet is really a letter by M. Francisque Michel respecting some new patterns of lightning conductors made by M. Jarriant, and submitted to the AcadÃ©mie des Sciences by M. le Comte du Moncel. The author states that there have been many theories as to the advantage of conductors rising to great heights above buildings, and that, on the other hand, some persons have urged that buildings should bristle all over with points, and thus prevent any disruptive discharge. He thinks that, owing to the translation of the storm-cloud by the wind, these short points will not always have time to act, and says that the only rational plan is to place a conductor high above the house it is intended to protect, and so constructed that it, and it alone, offers a path of scarcely appreciable resistance to the electric discharge. He says that in Germany they put a metal sphere on the top of the conductors, but in France, both the Academy and the Commission of the City of Paris have advised that they should terminate in a point.

M. Francisque Michel says that formerly a conductor was supposed to protect all objects within a cone whose base had a radius of twice the height of the conductor; but that he and M. FÃ©lix Lucas had investigated the question geometrically, and have arrived at the conclusion that the radius cannot exceed 1Â·75 of the height. Hence, in many buildings, it became necessary either to increase the number of the conductors or to make them more lofty, both alternatives leading to increased expense. M. Jarriantâ€™s design, which consists of galvanized angle iron bolted together, enables the increased elevation to be obtained at a price twenty per cent. below that of the old patterns. The angle irons themselves offer much surface, their angles are useful for discharging electricity, and they carry at the top the copper terminal recommended by the AcadÃ©mie.

(Abstracted by Prof. T. Hayter Lewis, F.S.A.)

â€œThe identity of electricity, manifested by friction, with that contained in the atmosphere, was not fully verified until Franklinâ€™s experiment with his kite in June, 1752.â€

â€œIn restoring the equilibrium between the opposite electricities of high potential, the discharge will pass by the shortest path, even though a poor conductor, in preference to a longer path through a good conductor.â€

The electricity of the earth is usually negativeâ€”of the atmosphere, usually positive.

He quotes experiments at Kew to this effect.

The friction of solid and liquid particles against the earth, and against each other in the air, produced by the wind, is a source of atmospheric electricity.

The height of the lower part of the thunder-clouds above the sea in the United States averages about 2,500 feet.

Dense thunder-clouds are good conductors, and are electrified to a certain extent by the induction of the electricity contained in the surface-earth. As electricity accumulates in the thunder-clouds it acts by induction on the surface-earth, and causes a corresponding increase of potential in the earth and the objects thereon.

He alludes to the vitreous tubes (fulgurites), 5 feet to 75 feet deep, as being formed by electricity passing to the subterranean water-bed through sand or other dry earth.

A highly positively electrified cloud within 3,000 feet of a building causes the latter to be intensely negatively electrified by induction.

So also the earth beneath the building and the upper portion of the subterranean water bed.

Whatever offers theleastresistance to the stroke will be its chosen path and it will never leave a very good line of conductors, which is in a short path between two opposite electricities, for an inferior one.

151 persons are killed by lightning annually in the United States, France, England, and Switzerland.

He quotes Sir W. S. Harrisâ€™s system for the Navy as preventive.

There is no absolute safety anywhere out of doors. It can only be found inside a structure having good conductors, with good earth connections.

Conductors cannot prevent disruptive discharge. They simply furnish a good path for lightning which passes over them without doing any damage.

Protective Area.â€”A committee appointed in 1875 by the Prefect of the Seine reports as protected, a circular space whose radius is equal to 1Â·45 [Should be 1Â·75, see page (67). Ed.] of height of conductor. But this is not always to be relied upon.

It is necessary that a conductor extend along the ridge, gable ends, and eaves of a house, and above each chimney.

Lightning is electricity of very high potential, and the difference of conductivity between the resistance of copper and iron to a lightning discharge is small and practically amounts to nothing.

Iron rod conductors not to be less than 7/16 inch diameter. No case is recorded where such a rod, properly connected with the earth, has been fused or greatly heated by lightning.

Paint or an ordinary amount of rust does not affect conductivity.

A conductor of large surface exercises a much greater protective action than the same quantity of metal in the form of a wire or solid rod.

Not because electricity in motion resides on the surface, but that the expansive action of a discharge may have a wider scopethroughthe metal.

So iron rain water-pipes are good conductors, and should be connected with metal spouting, conductor on ridge, &c.

Cable conductors bend easily and can be made in one length, so often answer better than bars.

If earth connection is good, rusty joints are of little consequence.

Conductors are not to be insulated.

Iron pipes for gas, water, heating, &c., also iron columns extending from basement to near the roof are to be connected with conductor and earth terminals.

The pipes on each side of gas meter are to be connected by iron bands.

Air terminals are to rise about 4 feet above each chimney or other elevated projection.

High steeples to have horizontal conductors round them at every 20 feet in height connected with vertical conductors.

One terminal in the centre of a building not over 25 feet long or wide is sufficient, or one at each end of the ridge. One to each 20 feet of a large building, with one at each end and to each chimney, &c.

When the horizontal portion of a lightning conductor, or path along the roof of a building from ridge to eaves (sic) exceeds 50 feet in length, the path becomes rather indirect for a lightning discharge, which is then apt to select a shorter route through the building.

The upper part of terminal need not be gilt.

Points are practically of no use.

Chimneys are very likely to be struck, owing to the heated air rising from them.

Provide against this by metal caps.

There is danger also, owing to the vapour rising from them, from barns stored with new hay or grain, stables, schools, churches, &c., containing many people, flocks of sheep, &c.

Earth terminals must be in moist ground.

The author quotes Prof. F. Jenkin as to the difference of conductivity between well moistened and perfectly dry earth (as porcelain, &c.) in electricity of low potential, as 1,000,000,000,000 to 1.

Gas and water mains usually 4 feet or so deep in dry earth, therefore not good conductors.

Examples quoted of injury to their joints by lightning, which passed from conductors to the mains.

Suggests, as earth terminal, an iron pipe, 10 feet long, 2 inches diameter, open at each end, perforated at sides, put in vertically, and having the water from pipes for rain and waste led into it.

To be 8 feet from foundation.

Gives engravings of numerous forms proposed for conductors, most of them being defective, and none show improvement on Franklinâ€™s round rod.

Copper rods held by iron staples, and connected with iron earth terminals, are bad, owing to galvanic action.

Copper wires in cable conductors become brittle, and snap when vibrated by the wind; sometimes, also, they are eaten away by electrolytic action.

He gives a drawing of a house protected as suggested by him, viz., by metal rain water-pipes connected with the metal gutters and ridge; also with his improved earth terminal by a good iron bar conductor.

Gas, water, and other pipes are to be connected together, and with conductor.

These often give better path for lightning than the conductors.

But dangerous if without proper earth terminal.

He disagrees with Prof. C. Maxwellâ€™s theory as to disconnecting the metal covering, &c., of buildings from the earth.

Lightning conductors detached from buildings do not afford absolute protection.

Lightning has great affinity for gas-holders, so one of the nearest guide columns should be connected by a metallic conductor with the pipe leading to street main, and also with a vertical earth terminal.

When a telegraph line is altogether metallic, well insulated upon poles, &c., and not metallically connected with the earth, the electricity of a storm-cloud will not exert so strong an inductive influence upon it as upon a line whose ends terminate in the earth.

Line wire is often melted, poles and apparatus shattered, and employÃ©s sometimes killed.

As a remedy, a galvanised iron wire is now fastened to every fourth pole by iron staples, from 4 inches above the top of the pole to a coil about 10 feet long of iron wire beneath its lower end.

(Abstracted by R. Van der Broek.)

In this pamphlet Dr. Karsten gives an account of two cases in which buildings that were provided with lightning conductors were damaged by lightning. The author states that the statistics for the year 1873 show that in Schleswig-Holstein twenty-six per cent. of all the cases of fire were caused by lightning; 1/130th part of these cases occurred in the towns and the remainder in the country.

Do lightning conductors guarantee absolute protection? The author answers this question as follows: There is no absolute certainty in empirical matters; each new case may direct our attention to circumstances that had been overlooked. If lightning conductors cannot be said to ensure perfect safety, they certainly afford a very high degree of protection.

The flash of lightning which struck the church at Garding, on the 18th of May, 1877, fractured the conductor in fifteen places and pierced the wall of the steeple in two places. The inefficiency of the conductor resulted from the carelessness with which it was fixed; the line was laid down the north side of the steeple and fastened with twenty-five wall eyes; these wall eyes were hammered too deep into the wall, thus damaging the line and forming a short and sharp bend in each case, besides also unduly straining the wire. The damage to the steeple was the consequence of a neglected secondary circuit. There are an excessively large number of tie-rods in the steeple; the heads of these rods are not connected together, neither are they, except in one case, in close proximity to any of the larger masses of metal that are about the building. The conductor passed close to one of those heads; the south side of the steeple, where the opposite head is, becoming wet through the rain, a secondary circuit was formed, and a return shock followed; the damage to the steeple was trifling.

The rod was provided with a conical point rather blunt but surmounted by a short platinum point. The copper line-wire was of good materialâ€”not of a uniform thickness, but at the weakest places not weighing less than 240 grammes per lineal metre (8 oz. per yard or rather less than Â¼ inch diameter if solid). The earth-plate was sunk into a well 10 metres deep, and tested faultless after the discharge.

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

This pamphlet opens with two pages devoted to the consideration of MichaÃ«lisâ€™s work published in 1783, â€œDe lâ€™effet des pointes placÃ©es sur le TemplÃ¨ de Salomon;â€ then it becomes more practical, refers to the Academy of Bordeaux propounding in 1750 the question as to the identity of lightning and electricity, and to Franklinâ€™s letter in the same year to Collinson, giving his reasons for believing in the analogy; states that the experiments suggested by him were repeated by Buffon and Dalibar in March, 1752, and subsequently repeated at Marly before Louis XV. Then the writer refers to the erection of the first conductor in France, to the popular displeasure which it excited, and to the long legal process before the proprietor was allowed to keep it in position.

The author thinks that in many cases it is better to slightly increase the number of conductors than to make them of excessive length, because the latter course causes them to fatigue and jar the roof timbers by their vibration with the wind.

Respecting platinum points he speaks strongly and to the following effect:â€”â€œI have already mentioned that Franklinâ€™s first conductor was melted. Since then, the upper terminals of conductors have been made of platinum, because it is the least fusible, the least oxidizable of all metals, and a very suitable one for making into points. Moreover, the sharper a point the greater its preventive action, and hence I condemn every conductor without a platinum point. Although some manufacturers employ simple copper cones, which may certainly last some time without deterioration, believing in the desirability of the points being always in perfect order, I reject their system entirely.â€

Few persons are used to making platinum points, it is a Parisian speciality, those which the author prefers, form a cone of about 10 degrees at the opening of the point and are about 1Â½ inches long, then screwed and soldered into a mass of copper forming a nut on the conical copper rod, which is 1 foot or 1 foot 6 inches long. The platinum point thus mounted can only give rise to a galvanic action so extremely feeble as not in the least to affect the durability of the apparatus. Some persons for the sake of cheapness suppress this platinum point, but they are wrong, the saving is slight and the result defective. The author objects to conductors made of bar iron because the joints are always defective, and if the section be too small they may be so heated as to set fire to the charcoal in which the lower extremity is buried.(!) However, the author prefers a rope, but he does not say whether of iron or copper, and he puts a strand of hemp in the middle so as to make it more pliable.

â€œArrived at the ground the conductor ought not to be in immediate contact with the earth, for the damp would slowly destroy it; we avoid this (?) by making it pass through a trough filled with coke. Experience has shown that iron thus buried in coke undergoes no change even during thirty years.... Broken coke is better than charcoal because of the great quantity of water which it absorbs.â€

The author then says that after passing through this trough the conductor must be continued into a well, or into very moist earth, and should end with a discharger like a fork with many prongs.

He recommends that all the iron be galvanized.

Although the concluding paragraph, coming from a manufacturer, sounds rather like self-recommendation, it undoubtedly contains important truths. M. Jarriant says:â€”

â€œI cannot too strongly advise that in erecting conductors those specialists should be employed, whose studies and constant practice enable them to ensure perfect work. It is necessary also that every workman should remember that in placing a lightning conductor he holds in his hands the lives of men, that he should feel conscientiously interested in the perfection of his work, and, finally, that he should feel that it is a mission which he fulfils, and not a mere matter of trade at which he works.â€

REPORT on THE LIGHTNING CONDUCTORS of the SMALL ARMS AMMUNITION FACTORY at DUM DUM, CALCUTTA.By W. P. Johnston.Government Telegraph Press. 1878. 4to.

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

This is an interesting report of a careful inspection and an electrical testing, by a skilled electrician, of the lightning conductors at this place. Although most carefully protected by well arranged and adequate copper rods, copper bands, iron rods, and iron tubes, and terminated in points, it was found that the points were covered either with rust or with paint, and that the earth connections were so bad as to render the buildings unsafe, although there was no difficulty in obtaining a good earth at any part of the factory.

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

A pamphlet by a distinguished American telegraph engineer, giving his view on the magnitude and origin of atmospheric electricity, which he attributes principally to the friction of air on ice in the Polar regions, and which circulates southwards in the higher regions of the air, and northwards in the crust of the earth. Hence also Aurora Borealis which is always preceded by high winds and most frequent when the earth is covered with snow.

Thunderclouds are usually about 2 miles high and from 13 to 23 miles thick. Lightning is much less frequent in mountainous than in plain countries. Copper lightning conductors are often applied to iron ships and iron buildings, but absurdly, as they are in such cases superfluous.

The author advocates immense earth plates where there are no gas- and water-pipes, which he calls the best lightning rods ever erected, because they are electrically in perfect connection with the earth. The track of a railway makes a capital earth. He has never known an accident where proper conductors were used, whereas he has known many accidents from imperfectly and improperly constructed lightning rods, though of the latest and most approved patents.

(Abstracted by Prof. T. Hayter Lewis, F.S.A.)

The authors state that a Municipal Commission has recommended, to the exclusion of all other points, copper about Â¾ inch diameter, terminating in a cone of 30Â°.

As to the area protected Messrs. Collin refer to the reports of the Academy in 1823 and 1854, admitting, as a limit of protected area,a circumference of which the radius equals double the height of the upper terminal for slightly elevated buildings, and simply the height for towers, &c., but this rule is badly defined.

The authors quote formulÃ¦ based upon the assumed altitude of the storm cloud, but state them to be unreliable.

The Academy in 1854 reports that an electrified cloud is equally attracted at equal distances by a metallic part of the roof and by the terminal of the conductor.

Exposed points of pinnacles, &c., are to be united to main conductors.

If copper be too expensive use iron wire.

The conductors are to be supported at about 10 centimetres (4 ins.) from walls and roofs.

The Academy recommends them to be isolated on glass or porcelain, but the New Commission rejects this, and suggests that all metallic parts be united to the conductor,â€”also recommends that wells be sunk to water level, as earth connections.

But this would often entail a depth of 20 to 100 metres, or even more. So the conductors may be sunk into moist earth and surrounded with coke, and if necessary, may terminate in a sheet of copper.

A good earth is very important. Connection with water mains advised.

The authors have fixed 8,000 lightning conductors on their principle without failure.

They give engravings of the various parts.

They engrave a diagram of a powder magazine which they propose to protect by a tall isolated lightning conductor fixed at a distance from it, and at such a height as that it will be included in a cone whose radius is equal to the height of the conductor.

(Abstracted by Alfred J. Frost.)

We learn that a lightning rod company in Cincinatti has patented a system of lightning protection, which consists of an iron rod running along the ridge of the building with points at each end projecting upwards. It is supported upon large glass insulators, and has no electrical connection with the building, and no rod running to the ground. It is said that there are many public buildings in Iowa which have been provided with this system of lightning rods.

Professor Macomber, of the Iowa Agricultural College, in reply to an inquiry, says that it would be possible that a house insulated with a glass foundation could be struck by lightning, but adds, â€œBy insulating a building the tendency to be struck by lightning would be very much lessened, and the severity of the shock much decreased. Practical illustrations of this can easily be obtained by means of an electrical machine. A spark can be made to pass from the machine to an insulated body, although the force of the shock will be much less thanwhen not insulated. Practically, it would be almost impossible to insulate a building, because after rain commenced to fall it would wet it so that communication with the earth would be established.â€

(Abstracted by H. Van der Broek.)

The author of this pamphlet, Prof. Dr. G. Karsten, states that thunderstorms are particularly dangerous in Schleswig-Holstein. He attributes that fact to the scarcity of woods in that province, not more than five per cent. of the surface being wooded; whilst in the Prussian empire the proportion of woods is twenty-three per cent.

Woods promote a uniform dampness of the atmosphere and lessen the up-current of air, which up-current contributes considerably to the formation of thunderstorms; and the woods thus cause the discharges of the electricity to take place principally between the clouds.

We do not yet know with certainty what the causes of atmospheric electricity are, but we do know under what conditions or circumstances thunderstorms may occur.

Thunderstorms are only formed when a violent condensation of the rarified particles of water, which the atmosphere contains, takes place. Such a sudden condensation, and the consequent formation of a thunderstorm, may occur when two different masses of airâ€”the one moist and warm, the other dry and coldâ€”intermix rapidly. The former of these currents we call the South, or Equatorial current, the latter the North, or Polar current. If these currents penetrate each other, or intermix slowly, long continued falls of snow and rain ensue; if they mix rapidly thunderstorms are formed during the warmer seasons, and sometimes also during the colder seasons.

The Schleswig-Holstein Provincial Fire Insurance Association alone paid, in sixteen years, the sum of Â£102,832 (an average of Â£6,427) for damages caused by lightning. This province loses altogether Â£12,500 per annum through fires caused by lightning.

The authorâ€™s very interesting remarks on the construction of lightning conductors are briefly summarised in the following general rules:

1. Copper and iron form the best materials for lightning conductors; lead and zinc may be used for secondary conductors. (Nebenleitungen.)

2. If the conductor be constructed of iron, it should weigh from 1,200 to 3,400 grammes per metre (2Â½ lbs. to 7 lbs. per yard), according to its length; a copper conductor should weigh, under the same circumstances, from 250 to 600 grammes per metre (Â½ lb. to 1Â¼ lbs. per yard).

3. The conductor must be connected with all the projecting corners and pointed parts of the building.

4. There must be no sharp curves or bends in the conductor.

5. The conductor must be connected with all the large andextensive masses of metal that may be about the building. This connection may be made by wires leading towards the rod, as well as in the direction of the earth contact.

6. The rods must be surmounted by good points, which must not be liable to be fused by the discharges of the electricity.

7. The height of the rods must be in proportion to the size and shape of the buildings; but it is better to erect several short rods than one extraordinarily long one.

8. In making the connection with the earth all sharp curves must be avoided.

9. The underground part of the conductor must be made of galvanized metal, so as to minimise the effects of oxidation, or, in case a layer of coke is used, to prevent the action of the sulphur.

10. The earth-contact should terminate in a plate, which, if possible, should always be immersed in water. If this can be so arranged the plate must have a surface â…’th of a square metre (1 foot square) for conductors for small buildings, whilst a plate of a surface of 2 square metres (5 feet square) will be sufficient for conductors for the largest buildings.

11. Where a permanent contact with water cannot be established, several plates of a larger size must be used, and laid in a stratum of coke.

12. In the case of very large buildings, provided with several rods and secondary conductors, several earth-contacts should be made which should be connected with each other.

With reference to the upper terminal point, the author remarks, in an appendix to the second edition of his pamphlet, that it should be made of a conical form of a basis of from 20 to 30 millimetres (0Â·8 in. to 1Â·2 in.), and of a length of 150 millimetres (6 inches); it must consist of pure copper and be gilded. It is useful to provide it with a platinum needle 15 millimetres (half an inch) long, and about 4 millimetres (0Â·2 inch) thick at its base; or with a cone of chemically pure silver, the proportion between whose base and height must be as 2 : 3.

(Abstracted by Prof. T. Hayter Lewis, F.S.A.)

Historical Factsâ€”

The following are brief references to some of the principal facts recorded in this volume:â€”

1600A.D.Dr. Gilbert showed that magnetic and electrical phenomena were emanations of one force.

1650. Otto Von Guericke constructed a little electrical machine (mainly of a ball of sulphur on a revolving axis).

Sir I. Newton constructed a machine of glass, but used it merely for amusement.

1675. The polarity of a shipâ€™s compass was found to be reversed by a stroke of lightning.

1708. Dr. Wall said that the light and crackling of rubbed amber seemed in some degree to resemble lightning and thunder.

1709. F. Hauksbee, F.R.S., showed the similarity between the electric flash and lightning.

1720. S. Gray, F.R.S., showed this by experiment, but was discredited.

1745. The first great step in this science was made at Leyden, by J. N. Allamand and P. van Musschenbroek, who discovered the properties of the Leyden jar. The priority of this invention disputed by Dr. Winckler, of Leipzig; a mania for experiments arose. Louis XV. tried them, unsuccessfully, on 180 of his Guards; but with perfect success on 700 Carthusian Monks.

1746.Dr. Franklin, of Philadelphia, saw some electrical experiments, and in

1747 received a glass tube and some books on electricity from London; then began to make experiments; sold his business, bought apparatus and made electricity his study. Discovered that electricity passed most easily and quickly through sharply pointed metals; that it was positive and negative; and that lightning and electricity were identical. He sent these results to the Royal Society, who refused to allow them to appear in their Transactions; he then published them in a pamphlet. It was not appreciated in England, but met with great applause in France, and was also translated into German, Italian and Latin.

1747. The subject was taken up in England in a thoroughly practical manner. Dr. Watson, Mr. Folkes, Lord C. Cavendish, Dr. Bevis, &c., experimented on a wire stretched across the Thames. The charge was found to come back by the water. The same result followed through moist earth. A gun was fired at a distance of four miles; the passage of the charge appearing to be instantaneous.

New experiments were made by Dr. Watson with glass rods, 2 and 3 feet long and 1 inch diameter. These showed that the rods, &c., contained electricity only as a sponge holds water.

1752. Experiments by Messrs. Dalibard and De Lor, at Marly-la-Ville, near Paris, in May, described.

1752. July. Franklin tried his Kite successfully, then his fame was established, and he erected, on his own house, the first lightning rod.

1753. Prof. Richmann, St. Petersburg, was killed whilst experimenting. The use of conductors opposed, violently in France, by AbbÃ© Nollet.

1755. An earthquake at Massachusets, was laid to the charge of the numerous lightning conductors. Franklin pushed their use by means of his publication, â€œPoor Richard,â€ which had an enormous circulation; particulars given showing success of lightning conductors.

1762. The first lightning conductor used in England, and Dr. Watson asked to send in designs for lightning rods for ships. He did so, but in an unpractical way, and they were disused.

1764. St. Brideâ€™s steeple struck.

1769. The Dean and Chapter asked Royal Society for advice as to protecting St. Paulâ€™s. Committee of Royal Society disagreed as to whether rods should be pointed. Pointed rods were used.

1769. The first conductor fixed to a public building in Europe was to a church steeple in Hamburg.

De Saussure, at Geneva, had some difficulty in explaining to the citizens that his conductors were not dangerous to his neighbours. There was a great fear, generally, as to their use,e.g., a lightning rod was erected, secretly, by the Priests at the Cathedral of Siena, and excited great terror in the townsmen when discovered, but a terrific stroke of lightning left the tower uninjured.

1772. Dr. Ingenhouszâ€™s experiments.

1774. The University of Padua protected by conductors.

1777. A building at Purfleet was struck though it had a conductor, but this was shown to be defective.

Sir J. Pringle had to resign his Presidency of the Royal Society because he advocated points, but experiments were made and ended in favour of points.

1778. The Venetians decreed that lightning rods should be erected throughout the Republic.

1819. Electro-magnetism discovered by Å’rsted.

1822. Sir W. S. Harris took up the question of providing good conductors for ships, and afterwards made a list of 250 accidents to ships in 40 years; also of 200 seamen killed or wounded in that time. At this time no importance was attached to the subject in England, except in the case of Sir W. S. Harris. He insisted on the necessity of lightning rods. A commission of inquiry was appointed by H.M. Government to investigate the best method of applying lightning rods to H.M.â€™s ships, and they reported (in 80 pages folio) that lightning rods were rather new fangled things, but might be tried, without special harm to anybody. So most ships were fitted with them after Sir W. S. Harrisâ€™s design. He was knighted in 1847. An iron built ship, metal rigged, is as well protected from lightning as Solomonâ€™s Temple. Harris combated the opinion of those who said that lightning rods attracted lightning.

Even in 1826 a government engineer recommended, on this ground, that all lightning rods should be pulled down, and, in 1838, the Governor-General of India ordered this by the advice of his â€œscientific officers.â€ This was not countermanded until several buildings had been destroyed.

Army circulars are now regularly issued, containing Sir W. S. Harrisâ€™s suggestions. (These quoted by Mr. Anderson).

Sir C. Barry suggested that Sir W. S. Harris should design lightning conductors for new Houses of Parliament. He reported in 1855. He used conductors of 2 inch copper tubes, â…›th-inch thick, to towers and other elevated parts, secured to masonry by metal staples. The cost was Â£2,314.

As to conductors, Le Roy recommended that they should rise not less than 15 feet above chimney and summit of any edifice.

Mr. Anderson gives technical names of parts of lightning rods in different countries. Chains first used, and gave rise to many accidents.Tin and lead conductors tried; lead especially, from its easy application to sharp curves, &c., but it is liable to be broken, and is a bad conductor; so it went out of use.

Some particular buildings are constantly under attack from lightning,e.g., Church of Rosenberg in Carinthia, not standing in a very high position, but greviously damaged in 1730, &c.; rebuilt in 1778, with lightning rod, and not injured since. Some of these effects may be explained on meteorological grounds: the height and thickness of the charged clouds only slightly varying, perhaps, in districts where there are prevailing winds. The height of clouds sometimes enormous. Instances are given of their being 15,000 to 25,000 feet above the sea. But sometimes clouds are almost flat on the earth, two instances are given of this. A remarkable and often fatal discharge is the â€œreturn stroke,â€ always less violent than the direct stroke, but often very powerful, and caused by the inductive action exerted by a thunder-cloud. Men and animals are charged with opposite electricity to the cloud. When the latter is discharged by the recombination of its electricity with that of the ground, the induction ceases, and all bodies charged by induction return to a neutral condition. Hence the dangerous â€œreturn stroke.â€ Lord Mahon first demonstrated this by experiment.As to originof atmospheric electricity, De Saussure considered it due to the evaporation of water by the sunâ€™s heat. Peltier (1765â€“1845) considered the earth itself to be one immense reservoir of electricity. As light comes from the sun, so electricity is generated by heat from the interior of the globe. No electricity is produced by atmosphere, nor held by it, except temporarily.

There is no recorded case in which a well made lightning rod, with â€œgood earth,â€ did not do its duty.

In 1822 there was an extraordinary number of thunder storms in France, so lightning rods were ordered by Minister of Interior for all public buildings, and he applied to the Academy of Sciences for advice. 1823. A Committee (Gray Lussac, &c.) reported. They laid it down, as a rule, that a lightning rod protected a circular area, having a radius of double the height of the rod; and they said nothing about regular inspection of lightning rods. So disasters occurred, and another Committee was appointed (Pouillet, &c.). They reported 1854. The theory as to the protected area was abandoned. It was recommended that lightning rods should have as few joints as possible. The joints to be well soldered, the points to be of copper (not platinum), and not to be very finely pointed. The rods to be of copper, not iron. The Louvre was well protected by lightning rods, but slightly injured, 1854. Another Committee was appointed, and, 1855, Pouillet again reported on its behalf. It recommended that the points (always of copper) should be thicker, and the rod to have a never-failing connection with water or moist earth, 1866. Several French powder magazines were struck though provided with lightning rods, and the Minister of War asked the Academy for another report. Another Committee (Becquerel, &c.) was appointed, and, 1867, Pouillet again reported. He defines lightning as an immense electric spark passing from one cloud to another, or fromcloud to earth, to restore equilibrium. The best protection for a building would be iron rods surrounding it on all sides, and passing deep into ground. Conductors should be inspected every year.

The conductor now remains essentially as Franklin invented it. Of the inner nature of â€œlightningâ€ we are utterly ignorant. The first conductors were always of iron as being cheap.

Sir H. Davy pointed out the different conducting powers of different metals. Becquerel, Lenz, Ohm, and Pouillet made similar investigations, with the following results:â€”

(The difference being owing, probably, to the greater or less purity of the Metals.)

1815. Brass wire rope generally used in Bavaria, but a steeple was struck down though with a brass wire conductor 1 inch diameter. The real defect was â€œbad earth,â€ but attributed to bad form of conductor; so this was abandoned. Brass not a reliable metal, and often destroyed by smoke. Purity of copper essential.

Professor Matthiessensâ€™ experiments shewed that the conductivity of copper varied fromâ€”

Hotel de Ville, Brussels, lightning rods designed by Professor Melsens on the principle of a great number of small ones in preference to one of large size, and covering building with network of metal, having many points and many earth contacts. He considers that the relation of section to surface of the lightning rod has a marked and definite, though unknown, result.

Author describes weathercocks and methods of fixing them.

Lightning rods generallyâ€”methods used in France: Terminal rods, usually of wrought iron, galvanized; their height depends on the size and area of building it protects. This is generally to be consideredto be within a cone of revolution, of which the radius = height of rod above ridge Ã— 1Â·75.

Points described. The conductors are of iron, rebated, soldered, and bolted at joints, with lead between. Bent plates of copper introduced to provide against contraction and expansion. In large buildings, metallic connections are formed on ridge by iron bars-Â¾ in. Ã— Â¾ in.

Precautions are taken against the destruction of iron underground, viz., by enclosing it in vertical sprints of wood, tarred or creosoted, rising a few inches above ground, or by a coating of tar or by a wrapper of sheet lead. The earth connection is a trough filled with broken charcoal, through which the conductor passes, ending in several branches, or in a grating between layers of charcoal. Galvanized iron cables sometimes used, and (rarely) copper of Â½ in. diameter.

America.Gutters and water pipes, &c., used where possible. If the roof be of wood, slate, &c., a conductor is laid along ridge, and connected with gutters and rain water pipes. If these latter be less than 3 in. diameter, the conductor is often extended from roof down the side of building close to the pipe. All metal chimney caps, railings, water and gas pipes, and other large or long pieces of metal, inside and out, are connected with conductor. The upper terminal usually projects 4 ft. above chimney or other highest part of building. It is a round rod, 7/16th in. diameter, hammered out to join it to conductor. A building 25 ft. wide and broad has one terminal in centre and one at each end. In larger buildings, one terminal to each 20 ft. of roof. Not always pointed.

Steeples have horizontal conductors at every 20 feet, connected with vertical conductors, to provide against discharge in centre, caused by deflection of discharge in the air by rain. Conductors are fixed to buildings by iron staples or straps; the earth connections are similar to ours. Also are used iron pipes, about 3 in. diameter and 10 ft. long, placed vertically in moist earth and carefully connected with conductor.

Newallâ€™s system: Copper conductors are the best, and in the end, cheapest. Terminal rods are usually 3 to 5 ft. long, and â…th to Â¾ in. diameter, branching out at top.

Germanâ€œreception rodâ€ described as being of iron, 10 to 30 ft. long; the area of protection theory discredited. The electric fire, seeking its nearest path to earth, is not to be diverged from it to the rod. These high rods of no use except,e.g., near high trees, and are often dangerous from being blown down. Barns containing new hay are likely to be struck, as hay sends out stream of warm air.

Designs explained for protecting private houses by short terminal points to chimneys, gables, &c. A copper rope at least â…th in. diameter should be used; a copper rod, Â½ in. diameter, has never been fused, so far as is known. In chimneys of manufactories, where rope is liable to corrosion, a greater thickness should be used.

Laughton-en-le-Morthen steeple injured, though with lightning rod, but this was only a small, thin copper tube, â…žth in. external diameter, and 1/32 in. thick; weighing 8oz. per foot, or equal to a rod about 0Â·12 in.diameter, the joints were corroded, and the earth contact was imperfect. Nevertheless, only one buttress was injured. It is of little consequence whether the conductor be inside or outside, if it be carried to earth by the shortest route. At first it was more generally put inside in France, but this was given up for fear of accidents. But it is beyond controversy that a good conductor is absolutely harmless to all surrounding objects, and a man might lean against a copper half-inch rod, carrying off a heavy stroke of lightning into â€œgood earth,â€ without being aware of its passing.

It is useless and dangerous to isolate conductors from buildings. All masses of metal should be connected with conductors.

Prof. Clerk Maxwellâ€™s theory described (as to disconnecting the conductors, &c., from the earth): He states that it is not necessary to connect masses of metal, as engine tanks, &c., if entirely within the building, unless a conductor as,e.g., telegraph wire, water or gas pipe come into the building from outside, then they must be connected with conductor.

List of accidents from lightning, also deaths or injuries in England and Wales, Prussia, United States, Sweden and Austria.

Particulars of damage to St. Georgeâ€™s Church, Leicester, 1846, and to West-end Church, Southampton. Also, to Merton College, Oxford, and St. Brideâ€™s Church, Fleet Street, none of these having lightning rods.

Wrexham Church struck, this had a copper conductor, but it was too small and the earth contact was doubtful.

List of buildings struck at home and abroad from 1589 to September, 1879, the authorities for the statements being given.

List of powder magazines struck between 1732 and 1878.

Earth Connections.Franklinâ€™s report, 1772, strongly urges the importance of this, in speaking of the powder magazine at Purfleet. In ordinary cases, moist earth is sufficient, but in such a case as this he recommends that a well should be dug at each end of magazine, with 3 to 4 ft. of water in it.

The importance of â€œgood earthâ€ is shewn by numerous accidents to buildings, as,e.g., in 1779, the church of St. Mary, Genoa, and, in 1872, the cathedral of Alatri, in which latter case, the discharge left moist earth to pass off by a water pipe, which it broke; but the church was uninjured. Also at Clevedon Church, where the conductor passed into a drain which was dry, but the stroke merely injured one buttress and passed off by gas and water pipes.

Mr. Anderson states that earth contacts must be large. That it is important that metal work be connected with lightning rod in at least two parts, to realize a closed metallic circuit, and so offer entry and exit. The earth contacts of the eight conductors of the Hotel de Ville, Brussels, described, viz., their being enclosed in an iron box, 8 in. Ã— 3 in. Ã— 3Â½ in., with three series of conductors (details given): one passing into a well, another to the gas main, the third to water main.

In ordinary buildings, the grating, with charcoal, coke, or cinders, &c., as before described, may be sufficient; but with large buildings, contact with water is absolutely necessary.

Periodical inspection.Author strongly urges this because conductors deteriorate from action of wind and weather above ground; the â€œearthâ€ often becomes bad, owing to new drains, &c.; buildings may be altered in regard of the quantity and position of metals. An instance is given of damage to a building owing to the change of position of iron safe. Conductors are often displaced by workmen; and the number and position of new gas and water mains, new trees, &c., also influence the power of conductors.

Appendix.This contains a very full list of books relating to lightning conductors.

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