REPORT OF THE SECRETARY 115 
day mean values of the solar constant of radiation as early and as frequently 
as results are available from its field stations in Chile and California. In 
general, results are available about 24 hours after the field observations. The 
Institution declines, however, to furnish regularly data of this kind to in- 
dividuals who may request them, since this would be in the nature of dis- 
crimination as between citizens, and, besides, too burdensome for the Institu- 
tion’s staff. 
Hitherto the values sent out daily have been stated to be “ Pre- 
liminary.” Since October, 1925, they have come from Montezuma 
alone. Considerable time must yet elapse before the data will have 
accumulated at Table Mountain sufficiently to permit of the statisti- 
cal study requisite before daily values can be received from that 
station. A definitive revision of all work since 1920 is now in prog 
ress, and when it is done all values hitherto published, and all those 
hereafter to be published, will be, it is expected, in their final form. 
Washington work—Revision of data.—As already remarked, much 
of the time of the director, Doctor Abbot, of Mr. Aldrich, and of 
the instrument maker, Mr. Kramer, was employed in connection 
with the preparations for the National Geographic Society Solar- 
Radiation Expedition Cooperating with the Smithsonian Institu- 
tion. This expedition will result in a very great increase of the 
value of the work of the two existing stations, by confirming or 
correcting their indications of solar variability. 
The remainder of the staff at Washington, comprising Mr. F. E. 
Fowle and Mrs. Bond, aided lately by Miss Marsden, who is em- 
ployed at the cost of private funds, have been at work on a com- 
plete revision of all Mount Montezuma data. The reasons for this 
are: (1) That with improved apparatus the basis for the existing 
“ short method ” tables had been modified; (2) that various improve- 
ments of methods of reduction have been discovered; and (3) that 
with a longer series of observations now available it is possible both 
to draw better curves for the “short method,” and to more accu- 
rately determine the systematic corrections required to eliminate 
traces of error still remaining, on account of atmospheric haziness 
and humidity. 
For these purposes about 125 days were entirely remeasured and 
fully rereduced by Langley’s fundamental method, used with newly 
devised precautions for exact results. From the excellent values 
of atmospheric transmission coefficients resulting, combined with a 
newly contrived function of atmospheric brightness and humidity, 
from which all influences of solar variation were removed by intro- 
ducing for the first time the pyrheliometer reading as a factor, a 
new basis was laid for the “short method.” Among other very 
valuable improvements the corrections for those regions of the spec- 
trum, not daily observed, which lie in the far ultra-violet and far 
infra-red were redetermined. 
