burgess: a micropyrometer 7 



Were there time, some further interesting deductions might 

 be given, as also some results of a preliminary study of the asym- 

 metrical portions of the Earth's magnetic field, not considered in 

 this paper. In conclusion, let it be emphasized that no claim 

 is made that the only possible mechanical description of the 

 phenomena has been given. It is quite possible to replace the 

 fundamental concept by some other; however, there still remains 

 to be found some adequate explanation for the disturbance 

 effects studied in this paper and provisionally referred to the 

 Earth's centrifugal action. The main purpose of the investiga- 

 tion is to discover a working hypothesis for guidance in the mag- 

 netic operations at present in progress, and to obtain clues as to 

 any possible additional data which may be required beyond 

 those usually obtained in magnetic surveys. 



PHYSICS. — A micropyrometer. George K. Burgess, Bureau 

 of Standards. 



Some time ago, a method was described^ suitable for the rapid 

 estimation of the melting points of minute specimens — as fine 

 as 0.001 mgm. or less. A microscope and an optical pyrometer 

 were sighted through a window of mica, or of plate glass in case 

 of melts in vacuo, simultaneously on an enclosed metallic strip 

 such as platinum, heated electrically and upon which was placed 

 the specimen to be melted. 



Evidently this apparatus may be simplified by combining 

 microscope and pyrometer into a single instrument, thus permit- 

 ting a single observer to watch the melting and measure its tem- 

 perature. This is effected by mounting within the Huyghens 

 eye-piece of an ordinary microscope a small incandescent lamp, 

 which is in series with a rheostat and ammeter. The tip of the 

 filament of the lamp is set to the same brightness as the platinum 

 strip viewed from above at the instant of melting of the metallic 

 or other specimen on which the microscope is focussed. The eye 

 of the observer therefore sees the specimen, the platinum strip 

 and the lamp filament all in focus at once and the current thru the 



1 Burgess, G. K., Melting points of the iron group elements by a new radiation 

 method. Bulletin Bureau of Standards, 3: 345. 1907. 



