2H BULLETIN OF THE 



in 1838, in which the principal governments of Europe were 

 induced to take an active part ; and had that of the United- 

 States, and those of South America, joined in the enterprise, a 

 series of watch-towers of nature would have been distributed 

 over every part of the earth."* 



A large collection of original notes of various meteorological 

 observations, — on magnetic variations, on auroras with attempts 

 at ascertaining their extreme height, on violent whirl-winds, on 

 hail-stones, on thunder-storms, and the deportment of lightning- 

 rods, — unfortunately never published nor transcribed were lost 

 (with much other precious scientific material) by a fire in 1865. 

 The phenomena of thunder-storms were always studied by Henry 

 with great interest and attention. A very severe one which 

 visited Princeton on the evening of July 14th 1841, was minutely 

 described in a communication to the American Philosophical 

 Society, November 5th, 1841. f 



On November 3d, 1843, he made a communication to the 

 Society "in regard to the application of Melloni's thermo-electric 

 apparatus to meteorological purposes, and explained a modifica- 

 tion of the parts connected with the pile, to which he had been 

 led in the course of his researches. He had found the vapors 

 near the horizon, powerful reflectors of heat ; but in the case of a 

 distant thunder-storm, he had found that the cloud was colder 

 than the adjacent blue space. "| 



On June 20, 1845, he read a paper before the Society on "a 

 simple method of protecting from lightning, building;s covered 

 with metallic roofs ;" urging the importance in such cases of 

 having the vertical rain pipes always in good electrical connec- 

 tion with the earth, since " on the principle of electrical induc- 

 tion, houses thus covered are evidently more liable to be struck 

 than those furnished either with shingle or tile." It is of course 

 necessary to have the metallic roof in good metallic connection 

 with the gutters and pipes; and the latter may conveniently 

 have soldered to the lower end a ribbon of sheet copper two or- 

 three inches wide, continuing into the ground surrounded with 

 charcoal and extending out from the house till it terminates in 

 moist ground. § 



In this paper he incidentally meets the much debated question 

 whether a lightning-rod is efficient as a conductor by its solidity, 



* Agricultural Report of Com. of Patents, for 1855, p. 367. 



t Proceed. Am. Phil. Soc. vol. ii. pp. 111-11(5. 



j Proceed. Am. Pliil. Soc. vol. iv, p. 22. 



§ Proceed. Am. Phil. Soc. vol. iv. p. 179. Henry appears to LavS' 

 been much impiesseii with the conducting value of the tinne^d sheet-iron 

 pipes commonly used as lain spouts, from observing that atnid the strange 

 vagaries of the circuitous path pursued bv the lightning (in cases of 

 honseg struck by this destructive ap;ent), the rain pipe was not unfre- 

 queiitly selected as part of the route ; — marks of explosive violence being; 

 exhibited at its lower en(J, und sometimes at its top as well. 



48 



