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.
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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 95.6 ohms at 16 deg. Cent. gave with a difference of temperature