740 THE POPULAR SCIENCE MONTHLY. 



until we reacli y, a star with a history. The components of this 

 celebrated binary are both nearly of the third magnitude, dis- 

 tance about 5'0", p. 150. They revolve around their common 

 center in something less than two hundred years. According to 

 some authorities, the period is one hundred and seventy years, but 

 it is not yet certainly ascertained. It was noticed about the be- 

 ginning of the seventeenth century that y Virginis was double. 

 In 1836 the stars were so close together that no telescope then in 

 existence was able to separate them, although it is said that the 

 disk into which they had merged was elongated at Pulkowa. In 

 a few years they became easily separable once more. If the one- 

 hundred-and-seventy-year period is correct, they should continue 

 to get farther apart until about 1921. According to Asaph Hall,, 

 their greatest apparent distance is 6'3", and their least apparent 

 distance 0'5" ; consequently, they will never again close up be- 

 yond the separating power of existing telescopes. 



There is a great charm in watching this pair of stars even 

 with a three-inch telescope not so much on account of what i& 

 seen, although they are very beautiful, as on account of what we 

 know they are doing. It is no slight thing to behold two distant 

 stars obeying the law that makes a stone fall to the ground and 

 compels the earth to swing round the sun. 



In 6 we discover a fine triple, magnitudes four and a half, nine,, 

 and ten ; distances 7", p. 345, and 65", p. 295. The ninth-magni- 

 tude star has been described as " violet," but such designations of 

 color are often misleading when the star is very faint. On the 

 other hand it should not be assumed that a certain color does not 

 exist because the observer can not perceive it, for experience 

 shows that there is a wide difi^erence among observers in the- 

 power of the eye to distinguish color. I have known persons 

 who could not perceive the difference of hue in some of the most 

 beautifully contrasted colored doubles to be found in the sky. 

 Such persons miss one of the finest pleasures of the telescope. In 

 examining 6 Virginis we shall do best to use our largest aperture,, 

 viz., the five-inch. Yet Webb records that all three of the stars 

 in this triple have been seen with a telescope of only three inches 

 aperture. The amateur must remember in such cases how much 

 depends upon practice as well as upon the condition of the atmos- 

 phere. There are lamentably few nights in a year when even the 

 best telescope is ideally perfect in performance, but every night's 

 observation increases the capacity of the eye, begetting a kind of 

 critical judgment which renders it to some extent independent of 

 atmospheric vagaries. It will also be found that the idiosyncra- 

 sies of the observer are refiected in his instrument, which seems 

 to have its fits of excellence, its inspirations so to speak, while at 

 other times it behaves as if all its wonderful powers had departed. 



