CURTIS: A VIBRATION ELECTROMETER 



567 



lowing among other results have been obtained as shown in the 

 table. 



For none of the metals examined was there a marked tempera- 

 tm-e coefficient in the range 900 to 2000°C. and for the most of 

 them this coefficient is negligible, the monochromatic emissivity 

 usually agreeing also with the value at 20°C. For the white 

 metals the emissivity usually shows very slight or no change at 

 the melting point, but for gold, silver, copper, and uranium there 

 is a marked discontinuity with red light. For palladium, there 

 are anomalies in the behavior of the emissivity in the region "of 

 the melting point, in that the value of emissivity proper to the 

 liquid may persist after freezing, constituting an undercooling 

 radiation effect. For platinum the fact that there is a change 

 in emissivity, for X = 0.65/x, on melting would influence the 

 constancy of the Violle standard of light as usually defined in 

 terms of the luminous radiation from platinum at its melting 

 point. 



Emissivities of Metals and Oxides with Micropyrometer 



PHYSICS.— A vibration electrometer.^ Harvey L. Curtis, 

 Bureau of Standards. 



Any alternating current measurement which makes use of a 

 null method requires an instrument which will detect small 



1 To appear in the Bulletin of the Bureau of Standards. 



