34 Mr. Ritchie on a Torsion Galvanometer. 



at the top, and then covered the inner surface of the bottom 

 with cement. A plate of zinc, of the same size with the 

 rectangle of copper, was placed exactly in the middle, hav* 

 ing a face of clean copper opposite each of the sides of zinc. 

 Copper wires being soldered to the rectangle of copper and 

 to the plate of zinc, and their ends dipped into the small 

 metallic cups of the galvanometer, the elementary battery was 

 then immersed in very dilute acid, and the torsion key turned 

 till the deflecting force of the battery was vanquished, the 

 number of degrees being about a thousand. Having removed 

 the battery, I covered one side of the plate of zinc and the 

 opposite surface of copper with cement, and repeated the expe- 

 riment as before ; when, as might naturally be expected, the 

 number of degrees of torsion were found to be very nearly five 

 hundred. We may, therefore, safely conclude that the double 

 plate of copper doubles the quantity of electricity without, of 

 course, altering its tension. 



Immediately after (Ersted's beautiful discovery of the mu- 

 tual action of magnets and Voltaic conductors, it was known 

 that an immense increase of electro-magnetic power is gained 

 by diminishing the distance between the copper and zinc 

 plates ; but, for want of a proper galvanometer, the law does 

 not seem to have been determined with that rigorous accuracy 

 which places its truth beyond the possibility of doubt. To 

 accomplish this was the object of the following experiment. 



EXPERIMENT IV. 



In order to avoid every source of inaccuracy, I procured a 

 rectangular wooden box, about a foot long, two inches broad, 

 and two and a half inches deep, into which plates of zinc and 

 copper two inches square might be fixed at any distance from 

 each other. Having filled the box with dilute acid, I placed 

 the copper plate at one extremity and the zinc plate at the 

 distance of nine inches, and observed the degree of torsion, as 

 in the preceding experiments. I then untwisted the thread, 

 placed the zinc at the distance of one inch from the copper, and 

 observed the degrees of torsion, which were now nearly three 

 times as great as before, This was next repeated with the 



