Augusts, 1900.] 



SCIENCE. 



173 



Some Peculiarities in the Eadial Velocities of 



S Geminorum : By W. W. Campbell. 



This is a well known variable star, period 

 of 10^ days. Its velocity in the line of sight 

 was found, independently at Pulkowa and 

 Mt. Hamilton, to be variable. Forty-five 

 observations at Mt. Hamilton, distributed 

 over 1 J years, left no doubt that this star 

 is a spectroscopic binary, and that the vari- 

 ation in brightness is produced by the com- 

 panion. The eclipse theory is untenable. 

 The variation is probably the result of tidal 

 action between the two bodies. 



The observed velocities cannot be repre- 

 sented by elliptic motion. Drawing the 

 elliptic curve which best represents the ob- 

 servations, the observed curve is alternately 

 above and below it, crossing it at intervals 

 of about 41 hours. Three complete periods 

 of the minor irregularities coincide with 

 one light period. These minor irregulari- 

 ties in the observed velocities are probably 

 due to minor tidal effects in the star's at- 

 mosphere. (To be published in the Astro- 

 phiisieal Journal) . 



H. M. Paul. I would like to ask if these 

 observations were plotted to represent the 

 total amount of observations, obtaining the 

 period from these observations. 



Mr. Campbell. They were all plotted 

 with reference to the brightness of the star 

 assuming the old period. There is some 

 doubt as to the exact form of the light- 

 curve. I have endeavored in every possible 

 way to ascertain the form of the light- 

 curve ; but there seem to be some irregu- 

 larities, and I think that extremely accurate 

 observations would show that the brightness 

 curve has the same irregularities as the 

 velocity curve ; that there is a reflex action 

 of one upon the other. 



G. W. Hough. Were there any syste- 

 matic observations to ascertain the cause of 

 irregularities with reference to motion in 

 the line of sight ? 



Mr. Campbell. No; we have obtained 



our results merely as by-products from the 

 system of guiding that we have employed ; 

 and we have made changes in the system 

 of guiding in the expectation that if we 

 could eliminate the difficulties arising from 

 that, so as to make it satisfactory for one 

 bright star, it would be satisfactory for two 

 stars. 



Mr. L. E. Jewell. Mr. Campbell has sug- 

 gested that the irregularity in the motion 

 in the line of sight may be due to tidal ac- 

 tion, which I think is probably the case ; 

 but he has also suggested that it may be 

 due to tidal compression, which I do not 

 think can explain the phenomenon. I have 

 myself been engaged in some work bearing 

 upon that problem, and among other things 

 the pressure of the different layers of the 

 solar atmosphere ; but the lines which have 

 been measured in the solar atmosphere do 

 not have a pressure of more than 1^ at- 

 mospheres, considering the pressure of the 

 earth's atmosphere as one. The variation 

 due to difference of pressure would be too 

 slight to produce the effect that he speaks 

 of. I think it probable some tidal action 

 causes the motion in the line of sight, 

 and that it is not due to change of pres- 

 sure, because the differences of pressure 

 would be too slight to produce such an 

 effect. In the case of the sodium lines in 

 the sun's atmosphere, the actual pressure 

 is only about an atmosphere and a quarter. 

 The variation in the hydrogen lines would 

 be very small, and it is probably produced 

 in a higher layer of the sun's atmosphere. 



Mr. Campbell. We seem to have no anal- 

 ogous case to this star from which to obtain 

 data to explain it. We have no knowledge 

 of tidal action elsewhere, but here we seem 

 to have enormous evidence of tidal action. 



T. J. J. See. I think the explanation of 

 the cause of the second curve superposed 

 upon the first curve is very probable. In 

 the case of the ocean tides, we have very 

 little vertical motion and a horizontal 



