The Telephone, Motograph, And Microphone - 8

The Telephone, Motograph, And Microphone - 8

In his researches to determine the nature of the motograph phenomena, and to open up
other sources of electrical current generation, Edison has worked out a very ingenious
and somewhat perplexing piece of apparatus known as the "chalk battery." It consists of a
series of chalk cylinders mounted on a shaft revolved by hand. Resting against each of
these cylinders is a palladium-faced spring, and similar springs make contact with the
shaft between each cylinder. By connecting all these springs in circuit with a
galvanometer and revolving the shaft rapidly, a notable deflection is obtained of the
galvanometer needle, indicating the production of electrical energy. The reason for this
does not appear to have been determined.
Last but not least, in this beautiful and ingenious series, comes the "tasimeter," an
instrument of most delicate sensibility in the presence of heat. The name is derived from
the Greek, the use of the apparatus being primarily to measure extremely minute
differences of pressure. A strip of hard rubber with pointed ends rests perpendicularly on
a platinum plate, beneath which is a carbon button, under which again lies another
platinum plate. The two plates and the carbon button form part of an electric circuit
containing a battery and a galvanometer. The hard-rubber strip is exceedingly sensitive to
heat. The slightest degree of heat imparted to it causes it to expand invisibly, thus
increasing the pressure contact on the carbon button and producing a variation in the
resistance of the circuit, registered immediately by the little swinging needle of the
galvanometer. The instrument is so sensitive that with a delicate galvanometer it will
show the impingement of the heat from a person's hand thirty feet away. The suggestion
to employ such an apparatus in astronomical observations occurs at once, and it may be
noted that in one instance the heat of rays of light from the remote star Arcturus gave
results.