XLIV. on Lightning and Gunpowder Magazines

Philosophical Magazine Series 5 ISSN: 1941-5982 (Print) 1941-5990 (Online) Journal homepage: http://www.tandfonline.com/loi/tphm16 XLIV. On lightning and gunpowder magazines Charles Tomlinson F.R.S. F.C.S. To cite this article: Charles Tomlinson F.R.S. F.C.S. (1889) XLIV. On lightning and gunpowder magazines , Philosophical Magazine Series 5, 28:174, 368-375, DOI: 10.1080/14786448908619877 To link to this article: http://dx.doi.org/10.1080/14786448908619877 Published online: 08 May 2009. Submit your article to this journal Article views: 7 View related articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=5phm20 Download by: [University of California, San Diego] Date: 22 June 2016, At: 15:49 [ 36s ] XLIV. On Lightning and Gunpowder Magazines. B~/ CHARLES TOMLINSON, F.R.S., F.C.S., ~'e.~ OME time about the year 1845 I visited the Tower of S London in company with a relative who was fond of architecture, and wished to inspect the remarkable Norman Chapel of St. John in the White Tower. We were informed that the Chapel was closed, on account of a great bulk of the Public Records being stored in it. The authorities~ however, allowed us to view it from an end gallery, which was partly choked up with dusty bundles of paper. We were informed that th.e vaults below the chapel were used as a gunpowder magazine. At this time the Duke of Wellington was High Constable of the Tower. When some one asked whether he was aware that some of the most valuable historical records of the kingdom were placed over the gunpowder magazine, the Duke replied, "I don't see what harm the Records can do to the gunpowder" ! In other words~ he was keeper of the gunpowder but not of the Records. Nevertheless the danger implied by the question was by no means illusory. In 1767 the Church of St./~azaire, at Brescia in Lombardy, was s~ruck by lightning, and a quantity of gunpowder belonging to the Republic of Venice, stored in the vaults of the church and estimated at 207,600 lbs. in weight, exploded, when not only the church but a considerable portion of the town was destroyed, and about three thousand persons werekilled. When the account of this disaster reached England our Government became alarmed as to the safety of our gunpowder magazines at Purfleet, which were qui~e unprotected against the attacks of lightning, and the Board of Ordnance sought the advice of the Royal Society as to the best means of protection. The Council appointed a committee, consisting of Dr. Franklin, the Hen. H. Cavendish, Messrs. Watson, Robertson, and Wilson, who inspected the magazines, and found them to consist of five buildings, side by side, each abou~ 150 feet long and 52 feet wide, built of brick and Downloaded by [University of California, San Diego] at 15:49 22 June 2016 arched under the roof, and standing on a chalk foundation. The Report, which was drawn up by Franklin, recommended an efficient system of pointed metallic conductors for each magazine, terminating at the lower extremity in a well of water to be dug at the end of each magazine. All the members of the committee signed the report except Wilson, who objected to pointed conductors on the ground that they drew the lightning to the building ; and he recommended blunt or Communicated by the Author. On Lightning and Gunpowder Magazines. 369 knobbed conductors as effectually answering the purpose of "conveying away the lightning safely, without that tendency to increase or invite it," that belongs to points. Wilson published a long defence of his view of the matter, and was ably answered by ~airne and Henley. Franklin admitted that "points drew electricity at a greater distance in the gradual silent way ; but knobs will draw at the greatest distance a stroke." Wilson found many supporters of his views, and the time of the Society was long occupied with discussions as to the respective merits of sharp and blunt conductors. Some even adopted the idea, which has survived even to our own time, that lightning-rods attracted the lightning to the building they were intended to protect, and thus occasioned loss instead of protection. This idea was started by the Abbd Nollet, who was for some time an electrical authority in France. In his Mdrnoire sur les effets du Tonnerre he expressed his opinion in the following terms :--" Toutes ces pointes de fer qu'on dresse en Fair ..... sont plus propres h nous attirer le feu du tonnerre qu a nous en preserver. The Board of Ordnance, however, resolved to adopt the Report of the Committee, supported as it was by such power- ful names, and accordingly proceeded to erect pointed conductors on the powder-magazines. The Report is dated 21st August, 1772. }Cow it so happened that on the 12th May, 1777, the Board-house at Purfleet was struck by lightning at a point upwards of 40 feet from the conductor. The damage was but slight, consisting chiefly of a few stones fastened by iron cramps being thrown down. A similar accident had occurred on the 17th June, 1774, when the chimney of a house at Tenterden was struck by lightning although another chimney 50 feet distant was furnished with a conductor. Such cases as these were made the most of by Wilson in favour of his knobbed conductors, although the whole contest between the sharps and the blunts involved a sort of fallacy, since, as Snow Harris puts it, " any termination which can con- veniently be given to a conductor, even if it were a ball Downloaded by [University of California, San Diego] at 15:49 22 June 2016 a foot in diameter, would be in relation to, say, a thousand acres of cloud, virtually, a pointed conductor." The mistake made by both parties in this controversy was in supposing that a lightning-conductor attracted the lightning ; whereas it is as passive as the rain-pipes destined to carry off the rain. Should a building or a ship form part of the line of least re- sistance between a thunder-cloud and the earth or the sea, the building or the ship will be struck ; but if they are furnished with properly arranged conductors, the lightning will pass Phil. Mag. S. 5. Vol. 28. ~o. 174. Nov. 1889. 2 E 370 Mr. C. Tomlinson on Lightning down without doing any damage, just as the rain passes down the water-pipe. By ~ properly arranged" is meant a conductor so fitted up that at whatever part of the building or ship the lightning may happen to strike, it shall be conducted safely to the earth or the sea. The French at one time had a theory that a lightning.rod protected a surrounding space equal to a circle the radius of which has twice the length of the lightning-rod. But in the presence of such cases as the above, and others that might be cited, the radius of protection theory has been abandoned by competent observers. But to return to our narrative. The continued opposition of Wilson and his party embarrassed the Board of Ordnance, and its members again applied to the Royal Society for advice. After considerable debate, a second Committee was appointed, consisting of the President and Secretaries together with Messrs. Henley, Lane, and NMrne. They examined the powder- magazines, and again reported in favour of pointed conductors. Whereupon Wilson contrived a number of experiments in support of his views, and forwarded a detailed account of them to the Board of Ordnance, which referred it back to the Royal Society. Several meetings were occupied in the reading and discussion of Wilson's paper, and at length another Committee was appointed, consisting of the I-Ion. H. Cavendish, Henley, Lane, Lord Mahon, Nairne, Dr. Priestley, and Dr. Watson, with instructions to test Wilson's experiments and conclusions, and report the result to the Society. The report was altogether unfavourable to Wilson, who became wroth at this further testimony in favour of Franklin's pointed conductors, and he endeavoured to persuade tile Government that the Society as a body did not agree with the reports of its several committees. Whereupon the Board of Ordnance applied to the President to ascertain whether this were so. The reply was to the effect that the voice of the Society was usually expressed by its Committees, but that in the present case " the Society had no reason to be dissatisfied with the Report of its Committee." England was at this rime at war with her American Colonies, and as the American rebel Franklin was the inventor of pointed Downloaded by [University of California, San Diego] at 15:49 22 June 2016 conductors, Wilson and his friends seized the opportunity of making the quarrel a political one. It is scarcely credibleat the present day that at the time here referred to I those who advocated sharp conductors were to be regarded as rebels and republicans, while those who advocated blunt conductors were naturally good and loyal subjects. Franklin was at this time in France, supporting the claims of the colonists in that country. In a letter to Dr. Ingenhousz, dated 14th October, 1777, after referring to the report which he drew up in 1772, a~M Gunpowder M-agazines. 371 and which expressed his own view and that of the other members of' the Committee as to the efficacy of pointed conductors~ he adds :q " I have no private interest in the reception of my inventions by the world, having never made, nor proposed to mak% tile least profit by any of them.

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