390 PROCEEDINGS OF THE AMERICAN ACADEMY 



lite, it will cut off ,, ., „ of its lijrlit, or produce a diminution in tlie 

 total liglit of -^ X 0.110 = 0.0G5. The secondary minimum would 



therefore reduce the light from 1.000 to 1.000 — 0.065 = 0.935, or 

 about 0.07 magnitudes. This will be the greatest effect, and would be 

 less if the transit was not central. An eccentricity in the orbit of 

 the satellite might even reduce it to zero by carrying the satellite at 

 superior conjunction entirely to one side of the star. 



The light reflected by the satellite from the star does not account 

 for this phenomenon, since during its transit the dark side of the sat- 

 ellite would be turned toward the observer. In no case would the 

 light reflected be sufficient, because the satellite does not receive one 

 ninth of the light of the primary ; so that, even if all were reflected, it 

 could not emit a -sufficient amount of light. 



A second hypothesis would explain the prolonged diminution of 

 light by admitting that the satellite consisted of a cloud of meteors so 

 scattered that about 0.110 of the liglit could pass through the central 

 portions. We should then expect that somewhat more light would 

 pass through the edges, and accordingly that the light would vai-y 

 slightly during the whole obscuration, attaining a true minimum when 

 the centres of the star and satellite appeared to coincide. 



In a recent note Dr. Vogel informs me that he has found no per- 

 ceptible approach or recession of Algol by means of the spectroscope.* 

 If this observation is conflrmed with the other similar variables, we 

 should infer that the masses of the eclipsing satellites were small, or 

 that the second hyjjothesis is the more probable of the two. In any 

 case, an excellent example is afforded of the value of indirect obser- 

 vations, like those with the photometer or spectroscope, in solving cer- 

 tain problems where direct measurements are valueless. 



The next step is to compare the results of other observers, and to 

 derive the correction to the ephemeris. Following the example of 

 Argelander by reducing to Paris mean time, the ephemeris for the 

 time at which any minimum will occur may be expressed by the 

 formula, — 



Time of miiiimii = 1880 June 23'» T" 44.0'» + 2'' IP SO-O" E. 



The number of minima which have elapsed since the discovery of 

 the variability is here designated by E, which accordingly equals zero 



* See also Ber. der Konigl. Sach. Gesell. xxv. 555, and Troc. Amer. Acad 

 xvi. 34. 



