June i, 1915] 



SCIENCE 



811 



soon to estimate the relative sensibility but 

 at least a tenfold improvement over the best 

 obtained with selenium is expected with 

 the new apparatus. 



We may now consider some of the more 

 strictly astronomical features of the work, 

 and the results to be mentioned were all 

 secured with the selenium- photometer. 

 There is one star in the sky which for a 

 hundred years has aroused more interest 

 than any other, namely, the well-known 

 variable, Algol. Once in 69 hours the star 

 is found to lose two thirds of its light, due 

 to the eclipse of the main body by a large 

 and relatively faint companion. This prin- 

 cipal eclipse has been known and studied 

 for a century, but it has often been pointed 

 out that if the eclipse theory is true then, 

 unless the companion is entirely dark, there 

 should be a second eclipse when it passes 

 behind the main body. This decrease in 

 light midway between the primary eclipses 

 was sought for in vain by visual observers, 

 but observations with the selenium photom- 

 eter established the presence of a diminu- 

 tion amounting to 6 per cent. There is also 

 a continuous variation between minima, 

 showing that the companion is brighter on 

 the side toward the primary, partly because 

 of reflection, but chiefly because of the heat- 

 ing effect. As the brighter body gives off 

 more than 200 times as much light as the 

 sun, it is easy to show that on the surface of 

 the companion nearest the primary there 

 is received more radiation per unit area 

 than is emitted by the sun, and even on its 

 fainter side, this body, which has often been 

 called dark, has much more than the solar 

 intensity. The scale of miles is not exactly 

 known, but each body has slightly more 

 than the solar diameter, the companion be- 

 ing a trifle larger, and the distance between 

 centers is less than five times the average 

 radius of the spheres. 



Another case is the second magnitude 



star, /3 Aurigce, which was one of the first 

 of the so-called spectroscopic binaries to be 

 discovered. As the spectrum lines are 

 single and then double on successive nights, 

 we have a system of two bodies with a 

 period of revolution of about four days. 

 The bodies will be in conjunction as seen 

 from the earth when the spectrum lines are 

 single, and this is the time to look for 

 eclipses. The photometric observations 

 show that exactly at the predicted times 

 the light of the system decreases 7 per cent., 

 the eclipses following each other at inter- 

 vals of half the period. "We have then a 

 twin system, each component having 2.6 

 times the diameter of the sun, 2.4 times the 

 mass, and being 1/7 as dense. The surface 

 brightness of each body is at least 12, and 

 possibly 25 times that of the sun, the total 

 light of the system being 150 to 300 times 

 the solar light. Therefore the sun if placed 

 beside these dazzling objects would look 

 like an insignificant dark body. 



The next star which has been observed is 

 S Ononis, the right hand one of the three 

 in the Belt of Orion. This object has given 

 us a great deal of trouble, and we have 

 spent something like two hundred hours at 

 the telescope in an effort to smooth out some 

 of the irregularities in the light curve. 

 There are two eclipses, one of 8 and the 

 other of 7 per cent., showing that the com- 

 panion is nearly as intense as the primary. 

 There is also a variation due to the elliptic- 

 ity of the orbit, the two bodies being 

 brighter when they are nearer together as 

 a result of a tidal or heating effect. The 

 larger body must have 5 times and prob- 

 ably does have 15 times the solar diameter, 

 while the companion is of half the linear 

 size of the primary. The total mass of the 

 system may be 20 times the sun's, and we 

 can say definitely that the mean density 

 of the system is 0.006 on the solar standard, 

 that is, the bodies average only 6 times as 



