of Edinburgh, Session 1877-78. 
559 
from the tuning-fork beside the proximal telephone, I found, that 
moving the latter away 3 or 4 inches from the vibrating fork, was 
followed by silence of the distal telephone ; indeed, to cause the 
latter to sound, the proximal telephone has to be placed as near the 
fork as possible. 
The following experiment is of interest, as showing the effect of a 
thin metallic disk in connection with the distal telephone : — Remove 
the disk, and apply in its place a plate of glass ; listen, and the 
sound of the proximal telephone will be heard faintly. Then put 
one of the metal disks on the glass, and on listening again, the 
sound will be found much intensified. It may be still further 
intensified by placing a second disk on the surface of the first, 
taking care to have a few morsels of paper interposed so as to pre- 
vent them from touching. 
The next step was to ascertain whether or not sounds could be 
heard at the distal telephone without the use of a disk there. 
There can be no doubt that sounds may be heard in these cir- 
cumstances. They are very faint, however, and have not the same 
quality as those heard with a disk. 
The arrangements at the distal telephone were further modified 
in the following experiment : — The disk was removed from the 
distal telephone ; and the base of a glass cylinder, 8 inches in 
length by 2J in diameter, filled with water, and closed at each end 
by a ground glass cover, was placed against the core. Very feeble 
sounds from the proximal telephone were heard, when the ear was 
placed at the other end of the glass cylinder. These sounds were 
slightly intensified by slipping in a thin metal plate between the 
base of the cylinder and the core ; but when a second disk was 
placed between the ear and the other end of the cylinder, the 
sounds were nearly as loud as with the ordinary telephone. In this 
experiment, the two disks were separated by a distance of 8 inches, 
and it is difficult to explain the phenomena as depending merely on 
conduction of sound. 
At this stage it occurred to me to place opposite to the core of 
the distal telephone a tuning-fork of the same pitch as that oppo- 
site the proximal telephone. The result was, that the one tuning- 
fork set the other in movement, so that the sound of the distal 
tuning-fork could be heard throughout the room. As is now known, 
