Mr. Ritchie on a Torsion Galvanometer. 33 



The instrument by which I ascertained the existence of a 

 Voltaic current from this elementary battery, consisted of a 

 greater number of coils in the rectangle, and the needles were 

 light and strongly magnetised. 



Having thus minutely described the torsion galvanometer, 

 I will now shew some of its applications ; but before doing 

 this it may be thought necessary to establish its accuracy, not 

 by reasoning (which is already done in the Philos. Trans.), but 

 by direct experiment. The following experiments will shew 

 in a striking manner the perfection of this instrument above 

 those formerly employed. 



EXPERIMENT II. 



Take two equal rectangular slips of copper and zinc, an 

 inch broad and eight or ten inches long, and divide them into 

 square inches by narrow bands of wax or cement. Solder 

 copper wires to their extremities, and fix them in a small frame, 

 so that they may always be placed at the same distance from 

 each other. Immerse them in a vessel of water, containing a 

 small quantity of sulphuric acid, to the first horizontal divi- 

 sion ; turn round the torsion key till the untwisting force of 

 the glass thread balances the deflecting power of the electric 

 current, and note the number of degrees of torsion. Immerse 

 them to the second division, turn round the torsion key as 

 before, and the degrees of torsion necessary to balance the 

 deflecting force of the current, from two square inches, will be 

 found double of those for one square inch. Repeat the experi- 

 ment with three, four, &c., square inches, and the degrees of 

 torsion will be found to be proportional to the surface of the 

 plates immersed. 



Having thus shewn experimentally the accuracy of the 

 instrument, I shall now apply it to determine the power 

 gained by Dr. Wollaston's contrivance of a Galvanic battery 

 above those formerly in use. 



EXPERIMENT III. 



Having provided a clean slip of copper, two inches broad 

 and about four inches long, I formed it into a rectangle, open 

 VOL. I. OCT. 1830. 



