84 
ASTRONOMY: C. G. ABBOT 
Proc. N. a. S. 
satisfactory for very long waves since both depend upon a knowledge of 
the absorption of blackened surfaces to long wave-lengths, and this is a 
matter which still lies in doubt. For satisfactory progress in this line of 
the measurement of nocturnal radiation, a new instrument depending 
upon the principle of the hollow chamber or absolutely black body ought 
to be devised. 
The study of the effect of ozone on the temperature of the earth is one 
which ought not to be neglected. Next to cloudiness and atmospheric 
humidity, ozone is thought to play the most important part in its effect 
on terrestrial radiation; first, because the quantity of ozone in the at- 
mosphere is believed to be variable, and, second, because its effect upon 
terrestrial radiation occurs near the wave-length 10 microns where water 
vapor is almost completely transparent. This research should include 
the determination of the variations of the quantity of atmospheric ozone 
and the measurement of the effect of its changes on the ozone band near 
10 microns in wave-length. 
A fuller discussion of the several points which have been raised above 
will be found in the following papers. 
INVESTIGATIONS IN SOLAR RADIATION 
Survey of the Present State of the Field 
We may inquire: First, what is the intensity of the radiation of the 
sun on which all the life of the earth depends; second, is this intensity 
constant or variable from day to day and from year to year, and what 
are the effects of variability, if any? 
1. The Solar Constant. — ^The question of the absolute amount of the 
solar radiation interests us not only for our own sake but for the sake of 
the future generations. What a valuable thing it would be if we knew at 
this time the intensity of the sun's radiation as it was in the times of the 
Egyptians and the Babylonians, and as it was in the intervening periods 
of Rome and the Middle Ages. It is plainly our duty to transmit to 
posterity accurate measure of the intensity of the sun's radiation as it 
is now, so that they will be in a better position in this branch of science 
than we find ourselves. We cannot expect to know the intensity of the 
sun's radiation as it would be in space at the earth's mean distance (that 
is, the so-called "solar constant of radiation") to that high degree of ac- 
curacy which we are accustomed to demand in many branches of physics. 
If we determine that value to one per cent, it is all we may reasonably hope 
for, because the intervention of the earth's atmosphere, with its changing 
amounts of haze and cloudiness will always interpose to the investigator 
an insuperable obstacle to the highest degree of accuracy. It may be 
that in the future apparatus can be shot up by means of rocket devices 
to go outside of the atmosphere altogether, but probably the sources of 
error of automatic apparatus for such a research will be found so large 
