JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V JULY 19, 1915 No. 13 



PHYSICS. — A direct-reading device for use in computing charac- 

 teristics of vacuum tungsten lamps.^ J. F. Skogland, Bureau 

 of Standards. 



It has been shown in a previous paper- that the ordinary char- 

 acteristic relations of vacuum tungsten lamps can be expressed 

 with high precision by a set of characteristic equations, each in- 

 volving two variables; or solutions can be made more quickly 

 by employing tables computed from the equations. For example, 

 having given observed values of voltage, candle-power, and watts 

 per candle, the values of Cp and wpc at any other voltage are 

 obtained from the equations or tables as follows: 



1. From the observed values of voltage and Cp their normal 

 values, that is, their values at normal wpc (1.20), are computed. 



2. The ratio of the desired voltage to the normal voltage just 

 found is computed. 



3. Substitution of this voltage ratio in the proper equations, 

 or reference to the corresponding point in the tables, gives a Cp 

 factor and the actual wpc. 



4. The normal Cp is multiplied by the Cp factor to obtain 

 the desired Cp. 



' Communicated by the Bureau. To appear in full as a Scientific Paper of the 

 Bureau of Standards. 



2 Middlekauff and Skogland, Characteristic equations of tungsten filament 

 lamps and their application in heterochromatic photometry, Journ. Wash. Acad. 

 Sci. 5: 61. 1915; Bureau of Standards Scientific Paper No. 235. 



453 



