ASTRONOMY: C. G. ABBOT 
383 
explanation through its relation to the deeps of the North Atlantic. 
Oceanica may be inteUigently linked up and explained. 
If the establishment of isthmian connections he explicable according to 
the discoidal theory, can their subsequent submergence also be accounted 
for? — According to the discoidal theory, the source of very large masses 
of igneous rocks lies in the base of the discs. The extrusion of the 
melt is accompanied by subsidence of the central portion of the disc, 
which in turn and in time may be succeeded by slipping down of the 
elevated margins. The mechanism appears to be workable. It re- 
quires, however, fuller elaboration than can here be given to elucidate 
it. These concepts are obviously consistent with the permanency of 
oceanic basins and continental masses. 
In addition to the tests proposed by these general questions, the 
theory should be tried by the more exacting requirements of the me- 
chanics of deformation. This has been attempted and not without 
reasonably satisfactory results. The structure of the Pacific ranges of 
California has been discussed before the Geological Society of America 
and the LeConte Club of California, and the paper will shortly be 
offered for publication. 
1 Abstract of a paper presented to the Geological Society of America at the Pasadena 
Meeting of the Cordilleran Section. 
RECENT SIMULTANEOUS MEASUREMENTS OF THE SOLAR 
CONSTANT OF RADIATION AT MOUNT WILSON, 
CALIFORNIA, AND CALAMA, CHILE 
By C. G. Abbot 
Smithsonian Institution, Washington 
Read before the Academy, April 29, 1919 
For the past fourteen years, with the exception of the year 1907, the 
Smithsonian Astrophysical Observatory has observed the solar radiation 
at its station on Mount Wilson, California, altitude 5700 feet. Meas- 
urements are m.ade by means of the pyrheliometer and spectro-bolometer 
at different hours of the day, so chosen that the intensity of the solar 
radiation as it would be outside the atmosphere at mean solar distance 
may be computed therefrom. During the earher years of the investi- 
gation it appeared that the values found vary from day to day, as well 
as from year to year. In other words, it seemed to be indicated that 
the sun is a variable star, having a two-fold variation. First, a varia- 
