207 
of 'Edinburgh, Session 1880 - 81 . 
also into a state of vibration, and so reproduce the sounds of the 
transmitter. To test the truth of this explanation, I have made 
the following experiments : — 
A cylindrical tin box, about four inches in diameter and two 
inches deep, with a tight-fitting lid, was provided. In the sides of 
the box three openings for corks were made — two being at the 
opposite ends of a diameter, and the third in a line at right angles 
to this diameter. Through the corks in the two opposite openings 
stout copper wires were passed, connected inside by a spiral of fine 
iron, or platinum wire. By this means the spiral was completely 
enclosed in the box, and the interrupted current from the trans- 
mitter could be easily sent through it. Through the third opening the 
box could be filled with water, or with any gas or vapour on which 
it was desirable to make experiments. The transmitter employed 
was either a tuning-fork interruptor, which vibrated 256 times per 
second, or the violin-microphone, and the battery power employed 
varied from ten to fifteen Groves’s cells. When the interrupted 
current from the fork was sent through the spiral of fine wire, it 
was seen, on looking through the upper opening, to glow with a 
beautifully varied glow, and on applying the ear to the end of the 
box, the sound of the fork was most distinctly heard. The box 
was then completely filled with water, and still the sound was 
heard almost as distinctly as before, accompanied, however, with a 
hissing noise. The electrodes carrying the spiral of fine wire were 
next removed, and replaced by two gutta-percha covered copper 
wires, so fixed as to leave a distance, inside the box, of about half 
an inch between their uncovered ends. The box was then 
completely filled with mercury, and the interrupted current sent 
through it, The current was thus made suddenly to heat and cool 
the line of mercury lying between the exposed ends of the 
electrodes, and this heating and cooling was distinctly recognised by 
the sounds heard when the ear was applied to the end of the box. 
The sounds, however, were not musical, although the tuning-fork 
was used, but consisted merely of dull thuds, arising, as it seemed 
from slow waves set up in the mass of the mercury. 
It struck me that, in this experiment, the action might be due partly 
to the repulsion between the end of the wire and the mercury produced 
by the self-induction of the current. To test this, I had a telephone 
VOL. xi. 2 D 
