Page:Popular Science Monthly Volume 84.djvu/115

Rh there was no official means of verifying the accuracy of clinical thermometers used by every physician in diagnosing disease. Here these thermometers are placed, perhaps a hundred at a time, in a bath of water whose temperature is controlled, by thorough stirring, to an equality of temperature of less than a hundredth of a degree. Of great importance is also development of a means of measuring high temperatures, such as those of red or white heat, at which glass would melt. For these high temperatures it is necessary to use a thermometer-bulb of platinum or some more infusible metal, and filled, instead of with mercury, with some gas. For practical purposes, such as the determination of the temperature of furnaces for porcelain, or for the treatment of steel or the annealing of glass, the temperature may be measured by the comparison of the color of the light emitted by the substances in question with that of a filament heated by a known electric current.

In the division of light one of the most important practical matters is the measurement of the intensity of sources of light, particularly of incandescent electric lights, for when one pays a certain amount he desires to get the largest amount of light possible for his expenditure. It is of interest to know that the amount of light obtained for a certain amount of electrical energy has been increased at least ten times in the last few years by the introduction of the filament of the metal tungsten instead of carbon. Another matter of practical importance in the division of light is the determination of the action of quartz crystal and other substances in twisting the so-called plane of polarization of light, since by this property the strength of sugar solutions is measured, and by such tests the rate of duty is fixed that sugar shall pay.

Two large buildings are devoted to electrical and magnetic research. The enormous development of the production of electricity, whether for light, power or transportation purposes, has rendered the exact specification of its standards of measurement of superlative importance. For over forty years such researches have been carried on in many countries, with ever-increasing precision, but still with certain small discrepancies between the determinations of different national laboratories. For instance, the unit of electric current is practically defined by the weight of silver that it will deposit from a solution in a given time. Owing to the discrepancies in the values obtained, the happy idea occurred to Dr. Stratton, the director of the Bureau of Standards, of inviting the national laboratories of England, France and Germany to send each a delegate to the Bureau of Standards in Washington, where each would carry on measurements by his own methods on the same current traversing all the instruments, thus the discrepancies were much reduced and physics was made to contribute to international good feeling. Besides these researches to establish the standards, which we have already seen to be necessary in heat,