108 Hare's Ekctrieat Plate Machine. 



ameter should be less. The deficit caused in the hand in 

 contact with the negative coating, is supplied by electricity 

 from the arm; and this, again, from the body, where if the 

 charge be inconsiderable, it is so much diffused as not to be 

 perceived. In like manner, a slight surcharge received 

 by the hand in contact with the positive coating, is diffused, 

 as it proceeds up the arm to the chest, so as to be too fee- 

 ble to be felt there. 



A piece of tin foil, interposed between paper, has been 

 found not to be perforated by a charge, which had pierced 

 the paper on both sides of it, 



If there were but one, current, it is alleged that tin foil, 

 iituated as above mentioned, would be pierced during its 

 passage from one coating to the other — a fortiori, then, it 

 should be pierced, if two currents be necessary, passing 

 each other. Besides, the explanation afforded, in the case 

 of a shock received by the hands, applies to this: owing 

 to its great conducting power, the tin foil diffuses the 

 attraction from each side, so much, as not to be dam- 

 aged by it. 



Abt. X[II. — Description of an Electrical Plate Machine, the 

 Plate mounted horizontally so as to show both negative and 

 positive Electricity. Illustrated by Engravings, By Ro- 

 bert Hare, M.D. Professor of Chemistry in the Univer- 

 sity of Pennsylvania. 



The power of electrical plate machines, has been gener- 

 ally admitted to be greater, than that of machines with cyl- 

 inders. The objection to the former has been, the difficul- 

 ty of insulating the cushions, so as to display the negative 

 electricity. Excepting the plate machine contrived by 

 Van Marum, I have read of none in which this difficulty 

 has been surmounted. It is still insisted upon, by respec- 

 table electricians, as if it had not been sufficiently removed 

 by his contrivance. 



I presume, therefore, that a description of a plate ma- 

 chine, by which both electricities may be shown, and 

 which, after two years' experience, I prefer on every ac- 

 count, may not be unacceptable to the public* 



'*.SeePlate— Fisr.S; 



