On Lightning-Rodx. ^31 



Art. XIX. — On Lightning- Rods. By Jeremiah Van 

 Rensselaer, M. D. 



Read before the Lyceum of Natural History, New-York. 



We hear so frequently of the destruction of lives and prop- 

 erty by the effect of lightning, that it is surprising; more 

 effectual measures are not taken to guard against its power. 

 In a country where the discovery was made, we should nat- 

 urally expect to find it in extensive use ; and yet England 

 and France are both more zealous than the government of 

 the United States in bringing to perfection the science of 

 Franklin, of whom it was well said, 



Eripuit coelo fulmea, sceptrumque tyraunis. 



The valuable report of M. Gay-Lussac on Parratonnerres, 

 orlightning-rods, has been published in the Annals de Chimie, 

 and may be advantageously consulted by translation in the 

 Annals of Philosophy. It was drawn up at the instance of 

 the French Academy of Sciences, and offers many very 

 interesting observations. 



The means proposed in the 3d Vol. of the American 

 Journal of Science p. 347, for the greater security of build- 

 ings, are fully adequate to that purpose, and should be exten- 

 sively adopted. With a view to draw public attention to this 

 important subject, perhaps the following observations may be 

 serviceable j premising that the papers of MM, Gay-Lus- 

 sac, de Romas, and Charles, contain a collection of valuable 

 and interesting observations so very generally found in the 

 able and lucid reports made to the French Academy. 



It is estimated that the velocity of electric matter, or of 

 lightning is at the rate of about 1950 feet per second : — that 

 it penetrates bodies, and traverses their substance with une- 

 qual degrees of velocity : that the resistance of a conductor 

 increases with its length, and may exceed that offered by a 

 worse but shorter conductor : — and that conductors of small 

 diameter are worse conductors than those of larger. 



The electric matter too tends to spread itself over con- 

 ductors, and to assume a state of equilibrium in them, be- 

 coming divided among them in proportion to their form, and 

 principally to their extent of surface ; hence a body that is 

 charged with the fluid, being in communication with the im- 



