1824.] M. Gay-Lussacon Conductors of Lightning. 427 



will not hold in (36) or (38), and, therefore, does not militate 

 against the general truth of my position, that the same expres- 

 sion may he periodic or non-periodic according to the form 

 under which it is put. 



John Herapath. 



Article IV. 



Instructions respecting Paratonnerres, or Conductors of Lightning. 

 Extracted from the Report of M. Gay-Lussac, in the name 

 of a Commission appointed hy the Royal Academy of 

 Sciences of Paris.*' (With a Plate.) 



The principal object of the report (which was drawn up at 

 the request of the Minister of the Interior), is to direct workmen 

 in the construction and mode of fixing conductors on buildings, 

 &c. It is divided into two parts, one theoretical, the other 

 practical. 



Theoretical Part. 



Principles respecting the Action of Lightning, or Electric 

 Matter, and of Conductors. 



Lightning is the sudden passage of electric matter through 

 the air, with the evolution of great light, from clouds highly 

 charged with that fluid ; its velocity is immense, far surpassing 

 that of a ball at the moment it leaves the cannon, and is known 

 to be at the rate of about 1950 feet per second of time. 



The electric matter penetrates bodies, and traverses their 

 substance, but with very unecpial velocities ; through some, 

 which are therefore called conductors, it passes with great 

 rapidity ; such are well burnt charcoal and water ; vegetables, 

 animals, and the earth, in consequence of the moisture they are 

 impregnated with, and saline solutions ; but, above all, metals 

 afford the readiest passage to the electric fluid. A cylinder of 

 iron, for instance, is a better conductor than an equal cylinder 

 of water saturated with sea salt, in the ratio of at least 100000 : 1, 

 and the latter conducts a thousand times better than pure water. 



Non-conductors, or insulating bodies, oppose great resistance 

 to the passage of electricity through their substance; such are 

 glass, sulphur, the resins, and oils ; the earth, stones, and bricks, 

 when dry ; air and aeriform fluids. 



No bodies, however, are such perfect conductors of electricity 

 as not to oppose some resistance ; which, being repeated in 

 every portion of the conductor, increases with its length, and 

 may exceed that which would bu offered by a worse but shorter 



» From tlie Annaksdc Cliimie. 



