684 THE POPULAR SCIENCE MONTHLY. 



have effect in reference to all public buildings and churches. The re- 

 port also became the chief authority on the subject in most foreign 

 lands. It likewise served the useful purpose of weakening the oppo- 

 sition, which still endeavored to maintain that disastrous explosions 

 were caused by conductors, and furnished clear and precise rules for 

 construction that were intelligible to ordinary workmen. 



In the year 1854 iron was much more generally used in buildings 

 than it had been at an earlier date, and some additional knowledge of 

 the conditions and laws of electrical action had been acquired. The 

 Academy, on this account, thought it well to request the Section of 

 Physics to reconsider the lightning-rod instruction of 1823. This led 

 to the first report, which was prepared by M. Pouillet, adopted by the 

 Academy of Sciences on March 5, 1855, and immediately afterward 

 issued by the Government as an additional instruction. In this docu- 

 ment it was held that the large masses of iron employed in buildings 

 certainly serve to attract the lightning. If two buildings of an equal 

 size were similarly placed, the one being exclusively of stone and 

 wood, and the other having large masses of metal in its construction, 

 the lightning would certainly strike the latter and avoid the former, 

 just as, when a ball of metal and a ball of wood are presented to- 

 gether toward a charged prime conductor of an electrical machine, it 

 is always the former, and never the latter, which receives the spark. 

 A dry soil, it was pointed out, does not attract the lightning. But, if, 

 under such a soil, there occur at some depth large masses of metal, or 

 accumulations of water, the lightning would explode through the dry 

 earth, splitting it up as a coat of varnish is pierced by an electric spark. 

 The line of lightning-discharge is always marked out for it before- 

 hand, in conformity with the law of electric tension, beginning at the 

 same instant at both the extremities of the track. The objects which 

 are most liable to strokes of lightning are good conductors that pro- 

 ject farthest over toward the clouds. 



In the report of 1855 the occasion was used to draw attention to 

 some instructive instances of the mechanical effects of lightning-dis- 

 charges which had taken place upon the open sea. In 1827 the packet- 

 boat New York, not at the time carrying a conductor, was struck dur- 

 ing its passage across the ocean, and a leaden pipe, three inches in 

 diameter and one inch thick, was fused where the discharge escaped 

 into the sea. A chain of iron wire, one quarter of an inch in diame- 

 ter and one hundred and thirty feet long, having been then hoisted up 

 on one of the masts and trailed in the sea, was struck by a second dis- 

 charge, and scattered into molten molecules and broken fragments, 

 the bridge being set on fire, although at the time covered by a sheet 

 of hail and a deluge of rain. The Jupiter, in the North Sea fleet, in 

 1854, carrying a chain of several strands of fortieth -of -an-inch brass 

 wire, two hundred and sixty feet long, hung from the mainmast-head, 

 and trailing seven feet into the sea, was struck, and had the chain 



