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SMITHSONIAN INSTITUTION 589 
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MADE BY BAKER-VAWTER CO. 
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It is probable that changes of temperature as small as one hundred-millionth of a degree were recorded in the work. Of course, it would have been impossible to have succeeded, even with such a wonderfully sensitive equipment without the great 100-inch reflector of the Mount Wilson Observatory to collect the light. 

The nine stars observed were Rigel, Vega, Sirius, Capella, Procyon, Aldeharan, Betelgeuse, Alpha Herculis, Beta Pegasi, representing all the principal types of starts from the blue ones down to the very red ones.

Astronomers have very definite impressions, based on other kinds of studies as to what sort of results might be expected from these heat spectrum investigations. But the outcome proved a great surprise. For instance, Vega and Sirius are classed together as both to spectrum type A[[subscript]]0[[/subscript]. That is, they are both blue-white hydrogen stars, with few lines showing in their photographic spectra, and both supposedly nearly twice as hot as our sun.

But Dr. Abbot's measurements proved that Vega has its maximum spectral heat a great way further toward the violet than Sirius , whose maximum heat is not very much nearer the violet than that of our sun. Still more remarkable is the blue star Rigel, for it shows to maxima. One occurs, as expected quite as far towards the violet of that of Vega. But the other, the greater one, occurs very near that of our sun.

The unanimous opinion of Dr. Hale, Dr. Adams, and the other Mount Wilson astronomers, is that this kind of study is to prove of the greatest possible scientific value and interest. For it gives a new lever, as it were, to attack the difficult task of learning to know the physical nature of the stars. All realize, however, that to get far with it many more starts of every type must be examined. Since there are too few very bright stars, this means that the apparatus must be made still more sensitive. In other words, if the present device can measure the hundred-millionth of a degree, the instrument
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