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LXIII. On the supposed Identity of the Agent concerned in the 

 Phenomena of ordinary Electricity, Voltaic Electricity, Electro- 

 magnetism, Magneto -electricity, and Thermo-electricity. By 

 M. Donovan, Esq., M.R.I.A. 



[Continued from p. 347.] 



Section V. 



HAVING now discussed the subject of the last section as 

 fully as seemed necessary, I proceed to a most important 

 branch of the investigation, one that is immediately connected 

 with the preceding. The instantaneous charge which a large 

 Leyden battery receives, by a momentary contact with an ex- 

 tensive voltaic series, has been always adduced as an argument 

 in support of the affirmed enormous quantity of electricity which 

 constitutes the voltaic current. The phsenomenon when first 

 discovered made a powerful impression on the minds of philo- 

 sophers, and a strong conviction has been the result. I never 

 was able to participate in this conviction ; and the first circum- 

 stance which raised my doubts was the feebleness of the shock 

 which a Leyden battery so charged is capable of communicating, 

 when compared with that given by the voltaic series with which 

 the Leyden battery was charged. Many years since, Sir H. 

 Davy induced me to take the shock of a Leyden battery charged 

 by a voltaic battery of one thousand pairs of zinc and copper, 

 each four inches square, then newly constructed for the Royal 

 Dublin Society : the shock was insignificant, and the spark 

 trivial. Accident afterwards gave me the shock of the thousand 

 pairs; it was the most tremendous sensation that can be con- 

 ceived, and nearly prostrated me. 



There are several accounts extant of the charge communicated 

 by voltaic series to Leyden batteries ; but many of the trials were 

 made with dry piles, or water batteries, or the contact of the 

 Leyden battery with the voltaic series was still maintained at the 

 moment of the discharge ; such trials therefore do not afford the 

 kind of information here required. There are however other 

 experiments on record relative to this subject, which supply 

 materials for strong arguments. 



Van Marum charged a Leyden battery of twenty-five jars, 

 containing a coated surface of 137^ square feet, by a momentary 

 connexion with a pile consisting of 200 pairs of silver coins and 

 zinc discs one inch and a half in diameter. It was charged to 

 the exact same tension as the pile itself, which was such as to 

 occasion a divergence of the gold leaves of Bonnet's electrometer 

 to the extent of five-eighths of an inch. The result was the 

 nme in many experiments. The shock given by the Leyden 



