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Here I have the mechanism, operated by the feeble current from the thermopile, opening and closing switches, and actuating bells and lights. Then, too, I have the recording instrument. The thing is fundamentally very simple and is based on well-known phenomena. It is not uncertain and can be tested at any time, just as I did then, when I showed a slight fall in temperature.
But the machine which you see here was one recently invented for registering the temperature of sea water so as to detect the approach of an iceberg. I saw no reason why it should not be used to measure heat as well as cold. "You see, down there I placed the couples of the thermopile beneath the electric furnace on the table.
Reliable determinations of the "energy" of the individual spectral rays were, for the first time, rendered possible by his invention of the "bolometer" in 1880. This exquisitely sensitive instrument affords the means of measuring heat, not directly, like the thermopile, but in its effects upon the conduction of electricity.
The spark of a factional or influence machine can be compared to a highland cataract of lofty height but small volume, which is more picturesque than useful, and the current from a voltaic battery, a thermopile, or a dynamo to a lowland river which can be dammed to turn a mill. It is the difference between a skittish gelding and a tame carthorse.
Gradually the light faded, as the thermopile adjusted itself to the change in temperature. Suddenly, without warning, a low-toned bell rang before us and a bright-green light flashed up. "That can have only one meaning," cried Craig excitedly. "Some one is down there in that inferno perhaps the bomb-maker himself."
Boeddicker, with Lord Rosse's 3-foot reflector and a Thermopile to measure the heat, and Mr. Frank Very, with a glass reflector of 12 inches diameter and the Bolometer invented by Mr. Langley.
He selected this mollusk because it was so abundant in the neighborhood of Naples, where, his experiments were made; and in making his experiments he made use of a thermopile, an apparatus by which, with the aid of electricity, much smaller quantities of heat can be indicated than by means of the most delicate thermometer.
As the room-walls had pretty much a uniform temperature, the deflection of the galvanometer was but slight, when the tube-axis of the thermopile was directed anywhere outside of the hot-air current rising from the flame. When, however, the axis was directed to this current, a deflection occurred, which was as great as that from the luminous flame itself.
At this end of the line I merely measure the electromotive force developed by the difference in temperature of two similar thermo- electric junctions, opposed. We call those junctions in a thermopile 'couples, and by getting the recording instruments sensitive enough, we can measure one one-thousandth of a degree. "Becquerel was the first, I believe, to use this property.
An ordinary lamp, with circular wick, and short glass cylinder, was wholly screened with a board, and a thermopile was so placed that its axis lay somewhat higher than the edge of the board.
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