"The accurate measurement of temperature is still a problem of considerable difficulty," he resumed, adjusting the thermometer. "A heated mass can impart vibratory motion to the ether which fills space, and the wave-motions of ether are able to reproduce in other bodies motions similar to those by which they are caused. 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.
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