man, and yet in the end as important to 

 him as any of lower limits. 



In short, then, the work of the Bureau 

 of Standards, aside from the protection 

 of the whole people from false measures, 

 may be said to be that of refining the 

 yardsticks of science. 



Here can be seen instruments of such 

 delicacy and precision that the mind at 

 first fails to grasp the full significance of 

 what they can accomplish. 



In one room is a balance so sensitive 

 that the mere presence of the operator's 

 body generates an amount of heat suffi- 

 cient to disturb its accuracy (see p. 153). 



In another there is one so delicately 

 adjusted that it shows the loss of weight 

 due to the reduction of the earth's at- 

 traction when two pieces of metal are 

 vv'eighed one upon another instead of 

 side by side (see page 161). 



Remarkable beyond the imagination 

 are the heat-measuring instruments which 

 register infinitesimal fluctuations of tem- 

 perature. A ray of light may have started 

 ten years ago from some distant star, and 

 may have spent all of those ten years 

 hurtling earthward-bound through space 

 at a gait so astounding that it could 

 girdle the globe in far less time than it 

 takes to blink the eye ; and yet when it 

 falls upon the sensitive bolometers at the 

 Bureau of Standards the}^ will tell the 

 observer how much heat that ray brought 

 with it from the star to the earth. 



Such are a few of the most delicate 

 instruments. But there are others wdiich 

 are as powerful as the}^ are sensitive. 



In the engineering laboratory there is 

 a huge testing machine which can tear 

 apart the strongest steel girders used in 

 building great sky-scrapers, Avhile on the 

 floor above are little electrical furnaces 

 capable of generating a heat intense 

 enough to melt the most refractory ma- 

 terials. The Bureau can measure accu- 

 rately cold great enough to liquefy the 

 very air we breathe, and heat which can 

 melt solid rocks (see also page 165). 



SUGAR COST-ING $15 PER POUND 



This is a commercial age, and even 

 this institution, so eminently scientific, 

 has something to sell. For example, it 

 will supply pure — absolutely pure — su- 

 gar for the trifling sum of $15 per 

 pound — under cost price, in fact ; and 

 yet, surprising as it may seem, there is a 

 ready sale. 



THIS MEASURES THE QUALITY OE A STARS 

 PI EAT 



This instrument, which is called a thermopile, 

 is here shown mounted so as to fit into the 

 eyepiece of a telescope. Its effective part is 

 the little black spot in the center, smaller than 

 the average pin-head ; j-et with its assistance 

 not onb' the quantit}-, but also the qualit^^ of 

 the heat given off b}^ a selected star can be 

 ascertained. The picture is enlarged to three 

 times the natural size of the instrument. 



But the average man may very well 

 say, "I can buy all the sugar I want at 6 

 cents a pound, and I have no earthly in- 

 terest in the quality of a star's heat; how 

 does this Bureau afl^ect me?" 



Directly it afl^ects him not at all ; indi- 

 rectly it touches him at almost every 

 hour of the day. Though he may not 

 know it, he probably pays for his gas by 

 the heat value fixed by that high-priced 

 sugar, his electric-light bulbs by the can- 

 dle-power determined here, his meats by 

 the weights, and his wanes by the meas- 

 ures the Bureau has standardized. The 

 imported sugar at his breakfast table, 

 the rails over Avhich he traveled to the 

 city, the concrete flooring in his fireproof 

 office building, the steel girder supporting 

 the roof above his head, all owe a debt 

 to the researches conducted by the Bu- 

 reau. 



NEW MEASURES CONSTANTLY COMING 

 INTO USE 



Formerly weights and measures were 

 restricted to length, area, volume, and 



157 



