HISTORY, &c., OF INDUCTION INSTRUMENTS. 



305 



" Lastly, the apparatus affords a valuable source of graduation in 

 the power to use either one or two elements, as they are inde- 

 pendent of each other. 



" Fig. 89 affords a general view of the apparatus ; it is entirely 

 contained in the box A, B, C, D, which is divided into two parts. 



Fig. by. — (Jliloride of silver battery. 



The first compartment contains the two elements which have been 

 described, L L', fixed between the sides of the box, by tlie springs 

 which serve to establish the communications. The second com- 

 partment contains the coil M, and its accessories. At one end of 

 the coil is the knob E of the graduator tube; at the other, a 

 trembler, which M. Gaiffe has ingeniously mudified. Instead of 

 its being regulated by a screw, which, in inexperienced hands, 

 often strains the spring, it is under the control of a bent lever, P, 

 which may be depressed to the position P', where it serves as a 

 pedal for the production of slow interru})tions, when pressed down 

 with the finger, so as to touch momentarily the small screw 0."' 



1 Le Roux, p. 5i', he. cit. 



