star systems. There are no doubt many blue and yellow stars having companions which have become so cool and nonluminous that their presence can not be detected photographically. To the eye the star will appear to be blue or yellow. A good illustration is the ordinary paraffin candle. To the eye it looks yellow, because the red-hot wick contributes but little to the total luminous output. But the red-hot wick is very rich in infra-red radiations, as compared with the luminous flame, and when measured with a thermopile (or some other similar radiometer), and an absorption cell, it is found that the red-hot wick contributes materially to the total energy radiated from the flame. In a similar manner a red-hot star will contribute materially to the total radiation from a star system which appears to be blue. The conspicuous star β Orionis (Rigel) is an excellent illustration. Astronomers have classified it "B 8 p" the letter "p" meaning that it has a peculiar spectrum. Whether this peculiarity is sufficiently definite to indicate that there is a companion star, the writer does not know. However, the writer's radiometric classification, Table II., would place it with the yellowish-red stars having a transmission of some 40 per cent, through the absorption cell, instead of with the blue stars. No doubt this star has a dark companion which has thus far escaped detection.
An excellent example which the writer desired to study, but was prevented owing to the fact that at that time (August, 1914) the star does not rise before dawn, is Sirius. This star has a companion which has become so cool that it is rated as a tenth-magnitude star. Although the presence of a companion star was suspected, the light coming from it is so weak that in the presence of the bright star (Sirius), for some years, it defied detection. This companion star is of enormous size, being one half as massive as the bright component; but it sends out only 1/30,000 as much light. It would have been very interesting to determine what amount of radiation from this star system is transmitted through the water cell.
Two stars having 5th magnitude companions were studied, viz., β Pegasi and α Herculis. Both stars appeared to have an excessive amount of total radiation in comparison with their photometric brightness. In the case of α Herculis the companion star caused a deflection of almost a centimeter on the galvanometer scale. In Table II. it will be noticed that this star has the lowest transmission through the water cell. No doubt this is attributable to the large amount of infra-red radiations contributed by the companion star, which caused galvanometer deflections about 1⁄5 those obtained from the bright component.
Attention has already been called to the fact that the receiver, which was attached to the thermojunction, was very small. It was therefore possible to measure the radiations from different parts of the surface of
