ening and closing the circuit.
To test this we disconnected the wire between the frog and battery, and
placed, instead of a vibrating sounder, a simple Morse key and a sounder
taking the 'etheric' from armature. The spark was now tested in dark box
and found to be very strong. It was then connected to the nerves of the
frog, BUT NO MOVEMENT OF ANY KIND COULD BE DETECTED UPON WORKING THE
KEY, although the brilliancy and power of the spark were undiminished.
The thought then occurred to Edison that the movement of the frog was
due to mechanical vibrations from the vibrator (which gives probably two
hundred and fifty vibrations per second), passing through the wires
and irritating the sensitive nerves of the frog. Upon disconnecting
the battery wires and holding a tuning-fork giving three hundred
and twenty-six vibrations per second to the base of the sounder, the
vibrations over the wire made the frog contract nearly every time....
The contraction of the frog's legs may with considerable safety be said
to be caused by these mechanical vibrations being transmitted through
the conducting wires."

Edison thought that the longitudinal vibrations caused by the sounder
produced a more marked effect, and proceeded to try out his theory. The
very next entry in the laboratory note-book bears the same date as the
above (December 5, 1875), and is entitled "Longitudinal Vibrations," and
reads as follows:

"We took a long iron wire one-sixteenth of an inch in diameter and
rubbed it lengthways with a piece of leather with resin on for about
three feet, backward and forward. About ten feet away we applied the
wire to the back of the neck and it gives a horrible sensation, showing
the vibrations conducted through the wire."

. . . . . . . . .

The following experiment illustrates notably the movement of the
electric waves through free space:

"December 26, 1875. Etheric Force.--An experiment tried to-night gives a
curious result. A is a vibrator, B, C, D, E are sheets of tin-foil hung
on insulating stands. The sheets are about twelve by eight inches. B and
C are twenty-six inches apart, C and D forty-eight inches and D and E
twenty-six inches. B is connected to the vibrator and E to point in
dark box, the other point to ground. We received sparks at intervals,
although insulated by such space."

With the above our extracts must close, although we have given but a few
of the interesting experiments tried at the time. It will