variable stars, especially those which undergo a change in color. A general radiometric survey of the stars is desirable; especially of star systems which may have companions which are too dark to detect photographically. The bright components of these stars would give an excess of total radiation as compared with other stars of the same color and having the same photometric brightness. Two stars apparently giving such an excess of total radiation were found in this preliminary survey and no doubt many other examples will be found.
It is possible that measurements of the total radiation from stars may be of assistance in answering the question whether light is absorbed in traversing interstellar space. When one considers that the measurements, made last August, on the radiations from Polaris (the pole star) were vibrations which were emitted forty-seven years ago, and that the radiations from the Orion group of stars started on their journey through space 160 years ago, the distances involved are so inconceivable that one naturally wonders how it can be possible that there is not sufficient "cosmic dust" in interstellar space to scatter and thus diminish the visible radiations to a greater extent than the invisible radiations; and yet the spectrographic evidence seems to be against this sought-for absorption of light in space. Another question awaiting solution is whether there is a "dispersion" of light in space; i. e., whether there is a retardation of say the violet rays as compared with the infra-red rays, so that the infra-red rays get here quicker than do the violet rays. This can be determined by measuring the radiation from an eclipsing variable star. If there is a retardation of some of the rays then the maximum and minimum of light emission should be different for different parts of the spectrum. This, however, opens up a new question of infra-red radiation from a dark comparison star, which may cause the eclipse, and it does not seem desirable to prolong this speculation.
It is an easy matter to indicate the problems demanding solution. It is quite a different matter to produce the instruments for their solution and in leaving now the discussion of the results obtained in the present investigation it is desirable to emphasize once more that the advance made thus far in developing astroradiometric instruments is very small in comparison with what will be required in order to make real progress in the work. For example, in the pioneering work of Nichols about fifteen years ago, the radiation sensitivity of his instruments was such that a deflection of 1 mm. would have been produced on his observing scale by a candle removed to a distance of five miles. The sensitivity of the radiometric apparatus used in the present work was more than 100 times as great, so that 1 millimeter deflection would have been produced by a candle removed to a distance of fifty-three miles. However, the real knowledge will not be gained by measuring the total radiation from stars, but by dispersing the starlight and meas-
