472 Mr. Snow Harris on Lightning Conductors. 



the spark determined, both in relation to the quantity and 

 surface over which it was distributed (/;), The form and 

 dimensions of the discharging conductor should have been 

 varied (r). The final electrical stale of his apparatus, as also 

 the electricity of the spark, should in common prudence have 

 been examined (Jc), together with other manipulations quite 

 inexcusable to neglect on such an occasion. He has, how- 

 ever, failed in everything calculated to give value to his in- 

 quiries, as 1 think has been fully shown. They are hence 

 not entitled to the smallest confidence, and it is not a little 

 extraordinary that he should have done so, whilst taking 

 credit to himself for superior sagacity^ and an acquaintance 

 with facts of which he says I did " not seem to be aware," 

 e. g. the most common-place facts in electricity. 



24. In conclusion, I have no hesitation in giving it as my 

 confirmed opinion, after a long and severe examination of 

 the laws of electrical action, and of cases of ships and buildings 

 struck by lightning; — that a lightning rod is purely passive, 

 that it operates simply in carrying off the lightning which 

 falls on it, without any lateral explosive action "whatever, ■ I do 

 not deny the general inductive effect mentioned by Lord 

 Stanhope on bodies opposed to the influence of the thunder- 

 cloud, and that the displaced electricity will again find its 

 equilibrium of distribution, and return to those bodies, which 

 effect would necessarily take place, whether we had a light- 

 ning rod or not (13); an additional reason for linking the 

 detached conductors in a ship's hull into one great mass, so as 

 to have as few interrupted circuits as possible in any direction. 



This opinion, by the citation of a few striking cases in 

 which ships have been struck by lightning, I liope in a future 

 paper fully to substantiate, should you think the subject of suf- 

 ficient consequence*. 



Appendix. 



The author, probably perceiving how little he had gained 

 by quoting Lord Mahon and Dr. Priestley, observes, in a sup- 

 plementary note, l)age 235, " Perhaps the experiments of 

 Professor Henry would be more to my purpose." These 

 experiments, however, are no more to "his purpose" than 

 the others, as any one may see who will examine the Profess- 

 or's communication, in the seventh report of the British As- 

 sociation, page 25. The experiments there described relate 

 to minor electrical discharges, similar to those already men- 

 tioned (i). These were obtained by throwing simple sparks 

 from an electrical machine, on small wires or rods, either 

 insulated or connected with the earth : the wires became lumi- 



[* We shall be most liapi)y to receive and insert any further communi- 

 cation from Mr. Harris. — Edit.] 



