A WONDERLAND OF SCIENCE 



165 



the aeroplane had ascended without a 

 careful study of each instrument ; for 

 one instrument recorded a height of over 

 2,000 feet, the highest reading, while the 

 lowest reading was 670 feet less, or 

 something under 1,400 feet. 



MEASURING HEAT BY EOOKING AT IT 



In the division charged with the stand- 

 ards of heat, researches are being con- 

 ducted which it is hoped will lead to in- 

 ternational agreement as to the standard 

 scale of temperature ; for, strange as it 

 may appear, only two points are at pres- 

 ent standardized, namely, the freezing 

 and boiling points of water; above and 

 below these nothing is fixed. 



Here the clinical thermometers used 

 by the medical profession are tested and 

 their accuracy to the tenth of a degree 

 certified, upward of 20,000 being han- 

 dled in the course of a year. Here are 

 tested the delicate Beckman thermome- 

 ters, which are used by chemists and en- 

 gineers in the trials on which the award 

 of large fuel contracts are based. The 

 high-temperature thermometers, reading 

 up to 1,000° Eahrenheit, and the low- 

 temperature pentane thermometers, used 

 for temperatures as low as 300° below 

 zero Fahrenheit, also receive their share 

 of attention. 



In another room is to be found ap- 

 paratus by which such intense cold can 

 be produced that even the air we breathe 

 becomes liquefied, and can be handled as 

 so much water. Put a bar of steel into 

 it and it will burn as if it were tinder, 

 in spite of the fact that the steel and the 

 air have been intensely cold. 



Hard by is another room where they 

 go to the opposite extreme, to the point 

 where we begin to realize the meaning of 

 the expression "fervent heat." Here the 

 hardest metals that exist melt as a pile 

 of snow before an April sun; and yet 

 they have to devise heat-measuring in- 

 struments as sturdy as the bolometer is 

 delicate, so that they can endure it and 

 register its temperature. 



In high-temperature Avork the Bureau 

 measures accurately heat up to the tem- 

 perature of the sun by means of compli- 

 cated and delicate instruments known as 

 pyrometers. These instruments are used 

 in manv industries ; for example, in the 



hardening, annealing, and tempering of 

 steel, the melting and pouring of molten 

 metals in foundries, the burning of ce- 

 ramics, the melting and annealing of 

 glass, etc., and many are tested and 

 standardized by the Bureau. 



High temperatures emitted by bodies 

 when they are incandescent or at red or 

 white heat are measured by optical or 

 electrical means. Thus, for example, the 

 bolometer measures by optical methods 

 very small amounts of radiant heat and 

 can record accurately changes of tem- 

 perature of less than a millionth of a de- 

 gree Fahrenheit. 



BENDING A STEEE BAR WITH ONE FINGER 



In the division of optics many tests 

 are made for the government and the 

 general public of telescopic and photo- 

 graphic lenses, prisms, samples of glass, 

 and optical instruments and accessories. 

 Work has been planned which will lead 

 to the standardization of the colors of 

 textiles, papers, tobaccos, butter, dyes, 

 liquors, and many other commodities. 



The fundamental basis of the work of 

 this section is the light wave. If all the 

 standards of length in the whole world 

 were by some accident destroyed, the 

 meter could be exactly reproduced from 

 the red line in the spectrum of cadmium, 

 as it is invariable, exactly 1.553,163.5 of 

 these wave-lengths forming the length of 

 a meter (see picture, page 160). 



Light waves form the unit of measure- 

 ment in one of the most precise instru- 

 ments known to science. This is the 

 interferometer, which can accurately de- 

 termine differences in length as small as 

 two-millionths of an inch, or measure- 

 ments so minute as to be beyond the 

 range of the microscope. 



To show the delicacy of this method, 

 the Bureau has evolved a remarkable 

 scientific device (see p. 160), with which 

 the visitor can see the bending of a steel 

 bar 3 feet long and 3^ inches in diameter 

 beneath the pressure of one finger. This 

 bar is supported at each end and a small 

 mirror is fixed at the center ; above it is a 

 frame bearing another partially silvered 

 mirror, both of which reflect the light of 

 a sodium burner, the lower mirror show- 

 ing a series of black and yellow concen- 

 tric rings (see Fig. A, page 161). The 



