Abstract
ATTENTION has been called in your valuable paper to the idea of registering cumulative temperatures by means of a pendulum, by M. von Sterneck, vol. xvii. p. 308, and this has called forth several letters. One gentleman has put forward my name as having devised means with some success. In an instrument exhibited at the Royal Society soirée, 1876, I could have left the matter resting at this point, but I am induced to write by the letter of your correspondent, “B”, in vol. xvii. p. 486, who says, “The chief merit in this matter will belong to the person who puts the idea into a working form which can be proved capable of giving accurate results.” As I think that I have fairly attained this end, or at least pointed out the way to it, with your permission I will describe the means which appears by the correspondence interesting to many of your readers. In my cumulative temperature clock the important element, the pendulum, is constructed as follows:—A steel cylindrical tube 32 inches long, 1¾ inch internal diameter, is hermetically closed at both ends. A rod is attached to one of the ends, which is placed uppermost, to connect this pendulum with the clockwork in the ordinary manner. An airtight division is made across the tube or chamber at 5 inches from the upper end. A small tube leads from this division to the bottom of the chamber. A conical plug is inserted in the upper chamber, to be hereafter described. A screw plug is placed under the small tube in the outer tube to enable the upper chamber to be filled with mercury. When the pendulum is so constructed, the lower screw plug is removed, and the upper chamber and leading tube filled with mercury by means of a small funnel. In this full state the mercury is boiled, and the whole inverted. It then becomes a steel barometer. To convert it into a thermometer, a small air-hole is made in the outer tube (this is not shown in the engraving), and this hole is closed up with a small air-tight cock filled with a porous material. When this is screwed on and turned off, it is isolated from atmospheric pressure, and the mercury rises into the upper chamber by any increase of temperature causing expansion of air in the tube, and sinks in the same manner by loss of temperature, so that the pendulum becomes simply an air thermometer. The pressure of the air by expansion within the tube in the rising of the mercury changes the centre of oscillation of the pendulum and accelerates the clock, and vice versâ.
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STANLEY, W. Cumulative Temparature. Nature 18, 41 (1878). https://doi.org/10.1038/018041a0
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DOI: https://doi.org/10.1038/018041a0
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