553 
of Edinburgh, Session 1877-78 
sounds. I am at present engaged in a series of preliminary experi- 
ments on this subject. 
3. Experiments with the Telephone. By James Blyth. 
Communicated by Professor Tait. 
In the telephones used in these experiments the permanent mag- 
nets were of the ordinary horse-shoe form, about 4 inches long. No 
cores of soft iron were attached to the poles, the insulated wire, No. 
26, being wound directly round both, in such a way that a current 
circulating through it followed the direction of Ampere’s currents. 
The vibrating disc was the bottom of a shallow can of thin tinned 
iron, 2J inches in diameter, supported directly above the poles of 
the magnet, and almost touching them. The receiving instrument 
was so arranged that any kind of disc could be easily substituted 
for the ordinary vibrating plate, and tested by sound from the same 
transmitting instrument, so as to allow of a comparison being made 
between discs of various materials. Having first ascertained that 
no sound was audible when no vibrating plate was used, I tried 
discs of the following substances, and have arranged them approxi- 
mately in the order of distinctness with which the sound was 
heard : — 
Ferrotype plate. 
Thin steel. 
Thin iron. 
Wire gauze (fine). 
Do. (a little coarser). 
Cast-iron plate, f inch thick. 
Sheet copper. 
Sheet brass. 
Sheet zine. 
With the view of testing what effect would be produced by varying 
the position of the wire coil on the leg of the magnet, I constructed 
a telephone, so that the coil could be easily slipped up and down 
the leg, while the sound was being sent from the transmitting 
instrument. Very little difference in the sound was observable till 
the wire coil was brought near the neutral point of the magnet. It 
Tinfoil. 
Vulcanite. 
Thin fir wood. 
Paper. 
Vulcanised India-rubber. 
Cast-iron, 6 inches thick. 
Slice of raw potato. 
Slice of fresh butter. 
