GALVANISM. 



this effect.* He found that a single 

 plate of zinc, of the size of a square 

 inch, when properly mounted, and sus- 

 pend'ed in dilute sulphuric acid, between 

 two copper plates of similar dimensions, 

 was more than sufficient to ignite a wire 

 of platina, one three-thousandth of an 

 inch in diameter, which formed part of 

 the connection between the two metals. 

 (8.) It will readily be conceived, that 

 by enlarging the size of the plates, their 

 power will be proportionally increased. 

 The first battery of this kind, on a very 

 large scale, was that constructed by Dr. 

 Hare, professor of chemistry in the uni- 

 versity of Philadelphia, and called by 

 him a Calorimotor, from its remarkable 

 power of producing heat.t It consisted 

 of sheets of zinc, and of copper, formed 

 into coils, so as to encircle each other, 

 separated only by interstices of a quarter 

 of an inch in width. This construction 

 is shown iufig. 3, which exhibits a hori- 

 Fig. 3. 



zontal section of the plates as they are 

 coiled together : the thick line Z, repre- 

 senting the zinc, and the thinner line C, 

 the copper plate. The zinc sheets were 

 nine inches by six ; the copper fourteen 

 by six ; more of the latter metal being 

 required ; as in every coil it was made 

 to commence within the zinc, and com- 

 pletely to surround it on the outside. 

 Each coil was about two inches and a 

 half in diameter ; their number amounted 

 to 80 ; and by means of a lever they 

 could all be let down at the same mo- 

 ment into as many glass jars, two inches 

 and three quarters diameter inside, and 

 eight inches high, placed so as to receive 

 them, and containing the acid liquor in- 

 tended to act upon the zinc. 



(9.) To the class of simple galvanic 

 circles must also be referred the magni- 



* See Thomson's Annals of Philosophy, vol. vi. 

 p. 209. While these pages were in the press we have 

 sustained an irreparable loss in the death of Dr. Wol- 

 laston, a philosopher whose unrivalled acuteness of 

 observation, soundness of judgment, and integrity of 

 mind, directed to the highest objects of science, place 

 his name among the mosteminent of its benefactors. 

 \ Silliman's Journal, iii, 105, and Annals of Phi- 

 New Series, i. 330,' 



ficent battery belonging to the London 

 Institution, and which was constructed 

 under the direction of Mr. Pepys. * It 

 consists of two plates only, the one of 

 zinc, and the other of copper, coiled 

 round a cylinder of wood, and prevented 

 from coming into contact by ropes of 

 horse hair, which is a non-conducting 

 substance, interposed in various places 

 between them . The length of each plate 

 is 60 feet, and its breadth two feet ; the 

 total surface being 400 square feet. In 

 order to charge this battery, the whole 

 coil is immersed in a tub containing 

 acid of the proper strength. 



CHAPTER III. 

 Compound Galvanic Circles. 



(10.) MANY of the effects of galvanism 

 require for their production the combined 

 influence of a number of plates, arranged 

 so as to form what is termed a com- 

 pound galvanic circle. To this class 

 belongs the galvanic pile, discovered by 

 Volta, and announced by him in a paper 

 which he transmitted, in the year 1800, 

 to the Royal Society. He had been led 

 by theory to conceive that the effect of 

 a single pair of metallic plates might be 

 increased indefinitely by multiplying 

 their ^number, and disposing them in 

 pairs, with a less perfect conducting 

 substance interposed between each pair. 

 For this purpose he provided an equal 

 number of silver coins, and of pieces of 

 zinc, of the same form and dimensions ; 

 and also circular discs of card, soaked 

 in salt water, and of somewhat less 

 diameter than the metallic plates, Of 

 these he formed a pile or column, as 

 shown in fig. 4 : in which the three sub- 

 Fig. 4. 



stances, silver,f zinc, and wet card, de- 

 noted by the letters S. Z, andW, were 



* Philosophical Transactions for 1823, p. 187. 



t Copper might have been used instead of silver, 

 as in the single galvanic circle already described, 

 ( 4, 5.)with the same effect. 



