Page:Popular Science Monthly Volume 79.djvu/218

214 every year state and city sealers of weights and measures for the purpose of discussing the best methods of securing the use of legal measures of all sorts, and the prevention of frauds by the commercial use of fraudulent weights. The frauds committed against the government by the sugar refiners were nothing in comparison with those perpetrated on the people by short weight in small commercial transactions.

The bureau has in the field a force of inspectors, cooperating with the state authorities in the detection of fraudulent weights and of short liquid and dry measures. Some of these are used innocently, but many show unmistakable fraudulent intent. The fifth annual conference on weights and measures adopted a resolution favoring legislation requiring that all containers be plainly marked to indicate their net content; also that authority be given to the Bureau of Standards by congress to pass on types of weighing and measuring devices used in trade.

The division of heat has had a particularly arduous task to perform. In contrast to the certainty and permanency of standards of length and mass, and of electrical quantities, there have been great discrepancies in temperature scales and the thermal constants depending on them. The standards used by different makers of thermometers were not in agreement with one another, nor did they agree with the accepted gas scale. There were marked differences even between the usual limits of freezing and boiling, or 0° and 100° C. When the work on thermometry was undertaken, a large per cent, of American-made thermometers for temperatures as high as 400° to 500° C. were subject to changes of 30° or 40° when exposed to the high temperatures they were designed to measure. Further, the average clinical thermometers, used so extensively by physicians, were subject to errors exceeding the limit of tolerance. At least 30 to 40 per cent, of the clinical thermometers on the market at the beginning of the work would have failed to pass the requisite test; to-day only about five per cent. fail. The bureau now tests many thousands of them annually. So great has been the improvement in American-made thermometers that the German makers are complaining more and more of the loss of American trade in thermometers; and some familiar types of mercury-in-glass thermometers are no longer classed as instruments of precision.

Not only has the bureau authoritatively fixed the scale ranging from 0° to 500° C, but it has met a demand for the accurate measurement of very high temperatures by investigating optical and radiation pyrometers, in which the temperature of an incandescent body is measured by the amount of light or heat emitted. The intensity of red light emitted by a body at 1500° C. is over 130 times as great as at 1000° C; and at 2000° C. it is more than 2100 times as great. Hence the possibility of a rough estimate of the temperature of hot bodies in the