Owing to the surface which the glass vessel exposes, the air inside
quickly responds to any external change of temperature, consequently
the apparatus is very sensitive. Another important feature is the fact
that the cradle and vessel in canting over acquires a certain
momentum, and thus the contact made becomes very certain.
[Illustration: PRITCHETT'S ELECTRIC FIRE ALARM.]
Mr. Pritchett proposes that his apparatus shall give external evidence
outside the house by ringing a gong, and by dropping a semaphore arm
released by an electromagnet. He also proposes (as has often been
suggested) that a water supply shall be automatically turned
on.--_Electrical Review._
* * * * *
A STANDARD THERMOPILE.
Dr. G. Gore, F.R.S., has invented an improved thermopile for
measuring small electromotive forces. It consists of about 300 pairs
of horizontal, slender, parallel wires of iron and German silver, the
former being covered with cotton. They are mounted on a wooden frame.
About 11/2 in. of the opposite ends of the wires are bent downward to a
vertical position to enable them to dip into liquids at different
temperatures contained in long narrow troughs; the liquids being
non-conductors, such as melted paraffin for the hot junctions, and the
non-volatile petroleum, known as thin machinery oil. The electromotive
force obtained varies with the temperature; a pile of 295 pairs having
a resistance of 95.
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