Experiments with Ekfirical Battety. [Book IVV 



die, it will, if the charge is ftrong, communicate mag- 

 ncdfm to the needle. 



If the difcharge of a battery pafies through a fmall 

 magnetic needle, it will deftroy the polarity of the nee- 

 dle, and fometimes invert the poles j but it is often 

 necefiary to repeat this feveral times. 



Dr. Priefriey could melt nine inches of fmall iron 

 wire at the diitance of fifteen feet, but at the diftance 

 of twenty feet he could only make fix inches of it red 

 hot, fo that we may infer from this, that notwitMtand- 

 ing their conducting power, ftill metals refift in fome 

 degree the .paSage of the electric fluid, and therefore 

 in eftimating the conducting powers of different fub- 

 ftances, their length muft not be forgotten. 



If a (lender wire is inclofed in a gla(s tube, and a 

 battery difcharged through this wire, it will be thrown 

 into globules of different fizes, which may be collected 

 from the inner ftirface of the tube ; they are often 

 hollow, and little more than the fcoria or drofs of the 

 metal. 



Dr. Watfbn and fome other gentlemen made feveral 

 curious experiments to afcertain the diftance to which 

 the electric {hock might be conveyed, and the velo- 

 city of its motion, which were briefly mentioned in the 

 firft chapter. In the firft experiment, the fhock v/as 

 given, and fpirits fired by the electric matter which had 

 been conveyed through the river Thames. In another 

 experiment, the electric fluid was made to pafs through 

 a circuit of two miles, eroding the New River twice, 

 going over feveral gravel pits and a large field, and 

 afterwards conveyed through a circuit of four miles, 

 This motion was fo inftantaneoufly performed by the 

 electric fluid, that an obferver, in the middle of a cir- 

 cuit of two miles, felt himfelf fhocked at the fame in- 

 ftant that he faw the phial difcharged. 



Notwith- 



