627 
of Edinburgh, Session 1877 - 78 . 
minating receiving action, where sending and receiving are on a par, 
is the disc of iron in front of the pole, almost hut not quite touching 
it — in fact, the disc of Bells telephone. 
Let us now retrace our steps, and go over the ground more 
minutely, beginning again with the coil. The coils I used consisted 
of from 30 to 100 ohms of copper wire '007 inches, and were of 
various sizes and shapes. For such fine wire coils, as already stated, 
one cell will suffice if the listener be sharp and attentive, but two or 
three must be used for easy hearing. The intermittent current 
given off by an ordinary medical electro-magnetic machine produces 
very audible sounds in such coils. The electric wave of such a 
machine is peculiarly adapted to excite telephonic sounds. It is a 
double wave of opposite name, with a sharp beginning and an equally 
sharp termination. For thick wire coils a more powerful electro- 
motor is required. With five fully charged Bunsen cells, I managed 
to get every coil I could lay hands on to render the ticking of the 
break, whether they had iron cores or not. The sounds were per- 
fect telephonic performances ; for it mattered not whether the wire 
was thick or thin, covered with silk or wool or cotton, the tick was 
not at all musical, but simply the reproduction of the sound of the 
break. We should be inclined at once to call such a rendering 
molecular, did we not know that in this era of mechanical telephones 
and phonographs, discs of tinfoil, oiled silk, paper, potato, butter, 
and other unlikely substances, can reproduce the tones of the human 
voice without peculiar accent. Coil ticking or tapping is familiar 
to any one who has dealt with a powerful induction coil. The sole 
of the instrument resounds with the primary coil rendering of the 
break outside the instrument. 
Now, whence comes this sound in a coil? Wiedemann, who 
gives De la Rive the credit of first noting the sound, attributes 
it to the clashing of the various convolutions against each other, 
due to the known action that wires conveying currents in the 
same direction attract each other. With a view to answer 
this question, I wound up 15 feet of '04 copper wire into 
a spiral f of an inch in diameter, and sent the intermittent 
current of a five-celled fully charged Bunsen battery through 
it. On holding the end of the spiral to the ear, I heard the 
tapping distinctly. On drawing out the spiral, so that no two 
