THE ASTROPHYSICAL OBSERVATORY—ABBOT 
strument have been made by our 
instrument maker, Andrew Kramer, 
which are in use in all parts of the 
world. An Argentinian observer, 
Enrique Chaudet, has confirmed our 
own experience with them, for he 
finds them highly stable in sensitive- 
ness over a period of 30 years, and 
capable of reading to an accuracy of 
one-fourth of 1 percent. We also 
devised the water-flow and the water- 
stir standard pyrheliometers. ‘The 
Se ae 
. 3 
SEs Se 
Sissies 
a 
ali 
‘a 
169 
able and thereby modify weather, 
came to us in 1903. Although the 
atmosphere over Washington, even 
45 years ago, was very unsuitable for 
attempting solar-constant measure- 
ments, we had been making them 
occasionally in 1902 and 1903 on 
cloudless days. Suddenly, in March 
1903, our results fell about 10 percent 
although carried on with the same 
instruments and methods as before. 
I made a statistical study of the 
Ficure 1.—Compensation water-flow pyrheliometer for standardizing instruments for 
measuring the intensity of the sun’s radiation. 
former we improved, as proposed by 
a Russian physicist, V. M. Shulgin, 
by employing two electrically com- 
pensated hollow chambers. With this 
improved instrument, L. B. Aldrich 
and I, in 1932, determined very 
accurately the absolute scale of the 
silver-disk instruments, used so gener- 
ally the world over, and often referred 
to as “the Smithsonian scale of 1913.” 
Our first inkling that the sun’s out- 
put of radiation, on which the earth’s 
temperature depends, might be vari- 
temperatures of all available parts of 
the Northern Hemisphere and found 
the exciting result that simultaneously 
with the slump in solar-constant re- 
sults there was a general fall of temper- 
ature from the normal over the whole 
North Temperate Zone. This work 
we showed to Secretary Langley and 
he published a paper on it.’ 
7™On a possible variation of the solar 
radiation and its probable effect on ter- 
restrial temperatures. Astrophys. Journ., 
vol. 19, No. 5, pp. 305, 307, 315-138, 321, 
June 1904. 
