298 THE POPULAR SCIENCE MONTHLY. 



ures made by different observers considerably exceeded 11*. Then 

 it began to close in, and in 1890 the distance scarcely exceeded 4". 

 Burnham was the last to catch sight of it with the Lick telescope 

 in that year. Since then no human eye has seen it. But during 

 its visibility its motions were so carefully studied that we can 

 have no doubt of its ultimate reappearance as it continues to pur- 

 sue its orbit around the center of gravity between it and Sirius. 

 According to Burnham, its periodic time is about fifty-three years, 

 and its nearest approach to Sirius should have taken place in the 

 middle of 1892. In that case it is now rapidly receding from peri- 

 astron, and news of its emergence from the rays of Sirius should 

 be expected at any time from Mount Hamilton, where a vigilant 

 outlook is maintained. If we can not see the companion of the Dog 

 Star with our instruments, we can at least, while admiring the 

 splendor of that dazzling orb, reflect with profit upon the fact that 

 although the companion is ten thousand times less bright than 

 Sirius, it is fully half as massive as its brilliant neighbor. Im- 

 agine a subluminous body half as ponderous as the sun to be set 

 revolving around it somewhere between Uranus and Neptune. 

 Remember that that body would possess one hundred and sixty- 

 five thousand times the gravitating energy of the earth, and that 

 five hundred and twenty Jupiters would be required to equal its 

 power of attraction, and then consider the consequences to our 

 easy-going planets ! Plainly the solar system is not cut according 

 to the Sirian fashion. We shall hardly find a more remarkable 

 coupling of celestial bodies until we come, on another evening, 

 to a star that began, ages ago, to amaze the thoughtful and in- 

 spire the superstitious with dread the wonderful Algol in 

 Perseus. 



We may remark in passing that Sirius is the brightest rep- 

 resentative of the great spectroscopic type I, which includes more 

 than half of all the stars yet studied, and which is characterized 

 by a white or bluish- white color, and a spectrum possessing few 

 or at best faint metallic lines, but remarkably broad, black, and 

 intense lines of hydrogen. The inference is that Sirius is sur- 

 rounded by an enormous atmosphere of hydrogen, and that the 

 intensity of its radiation is greater, surface for surface, than that 

 of the sun. There is historical evidence to support the assertion, 

 improbable in itself, that Sirius, within eighteen hundred years, 

 has changed color from red to white. 



With either of our telescopes we shall have a feast for the eye 

 when we turn the glass upon the star cluster No. 1454, some four 

 degrees south of Sirius. Look for a red star near the center. 

 Observe the curving rows so suggestive of design, or rather of 

 the process by which this cluster was evolved out of a pre-existing 

 nebula. You will recall the winding streams in the Great Nebula 



