134 



gray: temperature uniformity 



The Tessar and Cooke F/4.5 lenses gave results as follows: 



These tables show a fair constancy of transmission T as the 

 stop is varied. It may be noted further that the departure of 

 actual from indicated aperture ratio is the same'in the high speed 

 lenses of different makes. 



PHYSICS. — The production of temperature uniformity in an elec- 

 tric furnace. Arthur W. Gray. To appear in full in the 

 Bulletin of the Bureau of Standards, 



In the present paper certain improvements of the electric 

 furnace described several years ago by the writer^ are presented; 

 experimental evidence shows that it is possible in the new furnace 

 to heat a region of considerable length to any desired temperature 

 up to about 700° C. so uniformly that irregularities in the tem- 

 perature distribution will be less than the effect of heterogeneity 



» Joura. Wash. Acad. Sci. 2: 250. 1912. 



