444 THE POPULAR SCIENCE 2I0NTHLY 



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 photo- 

 graphically. 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 measure- 

 ments, made last Augiist, on the radiations from Polaris (the pole star) 

 were vibrations which were emitted forty-seven years ago, and that the 

 radiations from the On'o?i 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 sough t-f or 

 absorption of light in space. Another question awaiting solution is 

 whether there is a "dispersion" of light in space; /. 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 differ- 

 ent 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 solu- 

 tion 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 instru- 

 ments 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- 



