of Edinburgh, Session 1879 - 80 . 
703 
600 times a second, can affect the result, as what holds for one heat 
holds for all. I have not beside me a delicate microphone, but so 
far as I could judge from the rough one in my possession there was 
no difference in action between the break and it. ABCD is a key 
the handle of which, by virtue of its elasticity, rests on the stud B, 
but it can be pressed down on D and thus disconnected from B. 
The thread is stretched on two rods of glass rr, and the telephone 
may be held in the hand or placed on a supporting board. The 
current can take two courses according to the position of the handle 
ABC. As drawn in the diagram it can take’ the course 
cnhgmAWfeJclzn , or if the handle be pressed down, it takes the same 
as far as A from which it passes to D through K to I and z. In 
the first course both the wires gli and ef are included, in the latter 
only gh , ef being shunted out. To keep the resistance the same in 
the latter case, a platinum wire po, of the same length and thick- 
ness as ef is interposed. We have in the first case, as I view it, 
two opposing receivers on the extension theory or two sounders on 
the internal click theory. In the second case we have a receiver 
the same as that of Professor Chrystal. The sound emitted by the 
disc is much the same in loudness when both wires sound and 
when only one does ; if anything, I fancy it is in favour of the 
opposing wires. There is also a slight change in sound. When 
the experiment is so arranged that the wire itself passes through 
the disc, and we have a continuous wire from li to e, and when the 
key is readjusted to take off the current from m and lead it back to 
I, of course through a portion of wire equal to that shunted out 
4 p 
VOL. x. 
