THE PHYSICAL LABORATORY in 



there was no official means of verifying the accuracy of clinical ther- 

 mometers 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 tem- 

 perature 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 divi- 

 sion 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 labora- 

 tories. 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 inter- 

 national good feeling. Besides these researches to establish the 

 standards, which we have already seen to be necessary in heav^^*.-- 



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