Mabch 16, 1906.] 



SCIENCE. 



437 



other than those associated with mountain 

 sickness. In this region the railway reaches 

 an altitude of more than 14,000 feet, and some 

 of the moutains rise to more than 20,000 feet. 

 Probably no other part of the world can fur- 

 nish lofty mountains which are as accessible 

 as those of southern Peru and northern Chile. 

 Much of the extremely valuable work which 

 has been planned by Professor Hale for the 

 solar observatory on Mount Wilson, whose 

 altitude is 5,886 feet, could not be carried on, 

 perhaps, at an elevation of 19,000 or 20,000 

 feet; but for certain problems, especially that 

 of the solar constant, it may be that the future 

 will demand the fulfillment of the conditions 

 imposed by Dr. Langley. 



DOUBLE VARIABLE STARS. 



Two interesting cases have recently been 

 discovered by Mrs. Pleming, at the Harvard 

 Observatory, of double stars, both of whose 

 components are variable. That two variable 

 stars should be close together, where variables 

 occur in large numbers, as in the dense 

 globular clusters, or to a less degree in the 

 Magellanic clouds, would not be especially sur- 

 prising. Even here, however, as a matter of 

 fact, very few really close doubles are found. 

 In the sky as a whole, away from such special 

 regions, the number of known variables in the 

 40,000 square degrees of the sky is not much 

 more than 600, or one in 67 square degrees. 

 The chance, therefore, that two of them should 

 come within a few seconds of arc of each 

 other, unless there is some physical connec- 

 tion between them, is extremely small. 



The first double-variable consists of the well- 

 known variable star S Lupi and a close com- 

 panion, distant only 13", so close, indeed, that 

 it may often have been mistaken for S Lupi 

 itself, especially when it was bright and S 

 Lupi faint. 8 Lupi has a period of 346 days, 

 and varies in light about three and a half 

 magnitudes, between 9.6 and 13.1. The close 

 companion varies between 10.4 and 12.8, and 

 its period appears to be irregular. 



Another variable pair has just been an- 

 nounced. The components are 40" apart. 

 The first component varies between the magni- 

 tudes 10.0 and 10.6, and the second, between 



10.0 and 12.4. It will be of the greatest in- 

 terest to determine whether there is any rela- 

 tion between the light-changes of the com- 

 ponents, but this has not yet been possible. 



It is well known to astronomers that Mrs. 

 Fleming has discovered nearly 200 variable 

 stars by examination of photographic spectra, 

 made with an objective prism, in connection 

 with the Work of the Henry Draper Memorial. 

 By discovering that the spectra of long-period 

 variables usually contain the bright lines due 

 to hydrogen, she has been able to ' pick up ' 

 large numbers of variables of this class, while 

 engaged in other spectroscopic studies. It 

 would have been quite impossible for a single 

 observer, or, perhaps, for half a dozen, by 

 visual methods, to find such a number in a 

 lifetime. The results illustrate the .power of 

 photographic methods when the correct inter- 

 pretation has been found. In this, as in some 

 other lines of astronomical discovery, it would 

 be almost a waste of time for an observer, 

 unless for purposes of recreation or amuse- 

 ment, to carry on the investigation visually. 

 He would succeed about as well as a person 

 who should attempt to race on foot with a 

 fifty-horsepower automobile. This seems 

 really a pity, as there is undoubtedly a greater 

 charm, at least to the outsider, in the older 

 method. An observer sitting at a desk with 

 photographs about him, in a pleasant room 

 in broad daylight, appeals to the imagination 

 much less than the old-time astronomer, who 

 was supposed to sit through the long, cold 

 night with his eye glued to his telescope. 

 However, there are many fields in which the 

 visual observer still has the advantage. 



POSITION OF THE AXIS OF MARS. 



In a communication to the Monthly Notices 

 of the Royal Astronomical Society, Professor 

 Percival Lowell, director of the Lowell Ob- 

 servatory, gives an account of his observations 

 of the polar cap of Mars, for the determination 

 of the position of the martian axis. He also 

 compares the results of his own determinations 

 at three oppositions with those of Schiaparelli, 

 Lohse and Cerulli. From a study of all the 

 determinations Professor Lowell arrives at the 

 conclusion that the most probable values are 



