O^^ lAWS OF GALVANISM 



Inveftigatlon of nited half an inch of wire; 400 plates ignited two inches} 

 Afferent" iks in ?"^ ^^ P^^*®^ ^^ eight inch. fq. ignited 16 inches of the fame 

 burning wire. Wire. 



Now in order to accommodate thefe numbers to algebraic 

 palculation, we will fuppofe a comparifon of three batteries, 

 two of which are compofed of plates of equal diameters, but 

 differing in number ; the third Qiall alfo differ from the firft 

 jind fecond in the magnitude of its plates, and agree with the 

 fecond in the number of them. 



Let n be the number of plates in the firft, m the number in 

 the fecond and third batteries; w and y the diameters of the 

 two fets of plates. Then, if the power of any fingle plate 

 bear any conftant ratio to its furface, it will alfo have a con- 

 ftant ratio to fome power of its diameter, becaufe the furface 

 is as the fquare of the diameter in fimilar figures : let p be that 

 power ; let I, k, and z exprefs the lengthy of wire which are 

 ignited by the 1ft, 2d, and 3d batteries: then from the firft 

 datum, 71 : f?i :: I : k, becaufe the effedl is as the number of 

 equal plates, according to experiment. Again, feeing that w 

 js the diameter of the plates in the firft and fecond batteries, 

 and 1/ the diameter of thofe compofing the third, and p ex- 

 preffes the power determining the law of force for plates of 

 different diameters, the force of a plate in the firft and fecond 

 batteries, will be to the force of a plate in the third, as 

 stP : j/P, and as the number of plates in the fecond and third is 



Plate. Plates, 

 equal, we fhall have ?nw^ : my^ :: k : z, becaufe as 1 :m :i 



Plate. Plates. 

 lyP : k, and as 1 : m ii y^ : z, then as io^ : y^ :: k '. z, but as 



Ik: kz :: I: z =z 



.^'U^' gi 



?i : ?n :: I : k; therefore nm^ ; viy^ 



To apply this general theorem in order to determine the 

 value of p in all cafes, we will begin with your own experi- 

 ment made with equal furfaces on different numbers. 



Since 100 plates, of four inches, ignite half an inch of 

 wire, and 50 plates, of eight inches fq. ignite 16 inches, we 

 have n= \00, ?n = 50, w = 4-, yz=3, 1 = 1^, z= 16; there- 

 fore 100 X 4P : 50 X 8> : : 1 : 16 ; but fince 8 = 2x4, 8^= 



!''X 4P, therefore 2 : 2? 



16, and 16 =^=: 2^- 



but 



