218 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



THERMOMETERS 



It is well known that in the ordinary glass thermometers there is 

 an appreciable lag in the glass, so that successive readings in a de- 

 scending scale are inaccurate. To test the extent of this we have 

 placed a standard glass thermometer and a quartz thermometer of 

 our own construction in the same bath and raised the temperature 

 to 515° C. and then lowered it again to 0° C. In this particular 

 case the mercury in the glass came back to four divisions below the 

 zero mark, whereas the mercury in the quartz returned exactly to its 

 original calibrated mark at zero. While the capillary in the quartz 

 tubing is not exactly uniform throughout its entire length, it is so 

 uniform that a calibration of the tube over its whole length would 

 eliminate any inaccuracies due to the slight nonuniformity. 



TUNING FORKS 



As a standard of pitch the tuning fork is about the only appliance 

 in use. Temperature changes affect the pitch of the hardened steel 

 fork, however ; and, what is more important, the work which has to 

 be done in adjusting these steel forks to the desired pitch by grind- 

 ing or otherwise working them, results in changes in elasticity and 

 dimensions that cause a disturbance of the pitch note. A tuning 

 fork of quartz is not subject to these changes to any appreciable 

 degree. 



This work has all been carried on in the research laboratory of the 

 General Electric Co. at Lynn, and in presenting this description the 

 author wishes to express his appreciation of the efforts of Mr. L. B. 

 Miller and Mr. P. K. Devers, who in a large measure were respon- 

 sible for the good results obtained. 



