FEB. 19, 1923 PROCEEDINGS: PHILOSOPHICAL SOCIETY 65 
PROCEEDINGS OF THE ACADEMY AND AFFILIATED 
SOCIETIES 
PHILOSOPHICAL SOCIETY OF WASHINGTON 
872D MEETING 
The 872d meeting was held in the Cosmos Club auditorium, Saturday, 
November 18, 1922. It was called to order at 8:25 p.m. by President 
CRITTENDEN, with 40 persons in attendance. 
Mr. C. E. Van OrstraAnp addressed the Society on Deep-Earth tempera- 
tures in the United States. The address was illustrated by lantern slides, 
and was discussed by Messrs. CRITTENDEN, HryL, Paw1ina, Giscu, WHITE, 
Humpureys, Press, and HAWKSWORTH. 
Author’s Abstract: The application of electrical methods to the determina- 
tion of temperatures at great depths was discussed, but the instrument which 
seems best adapted for general use in making a geothermal survey is the maxi- 
mum thermometer. Apparatus for use in connection with maximum ther- 
mometers was described. Tests in a great number of wells show that an 
accuracy of 0.1 or 0.2°C. can be obtained when working under favorable 
conditions. The chief source of error is the lack of temperature equilibrium 
in the wells. 
A brief discussion of the data of observation from mines, and both flowing 
and non-flowing wells, was given. This feature of the investigation has not 
yet been carried to a point where definite conclusions can be stated. 
A paper by K. S$. Gipson and E. P. T. Tynpatu, on The Visibility of Radi- 
ant Energy and illustrated by lantern slides was discussed by Messrs. 
PawLinG, Press, and CRITTENDEN. 
Author’s Abstract: By the visibility of Radiant Energy is meant the 
ratio of luminosity to radiant power at the different wave-lengths (or fre- 
quencies) in the spectrum. In cooperation with the Nela Research Labora- 
tories, a new determination of this function had been made at the Bureau of 
Standards. The so-called “step-by-step”? method was used, which is an 
equality-of-brightness simultaneous-comparison method, in which there is 
little or no color difference in the two parts of the photometric field. Fifty- 
two observers were tested, some of them common to previous investigations. 
The final results are not greatly different from those obtained in other 
investigations, and comprise further evidence on the comparison of equality- 
of-brightness and flicker photometry. 
INFORMAL COMMUNICATIONS 
W. J. Humpureys referred to the various factors that appear to enter 
into the determinations of latitude. Among others, it had recently been 
found in England that there appears to be a variation of latitude with the 
velocity of wind. The question was further discussed by Messrs. Wuite, 
LAMBERT, and PAWLING. 
Mr. Paw.ine reported that recently he had made a setting with a tele- 
scope at the U. 8. Naval Observatory on a star that apparently was not 
catalogued. He was uncertain whether it was a variable start, or one that 
had been accidently omitted from the Star catalog. 
