5 i2 THE POPULAR SCIENCE MONTHLY. 



and that of the shorter 60". Closely following the nebula as it 

 moves through the field of view, our five-inch telescope reveals a 

 faint star of the eleventh or twelfth magnitude, which is suspected 

 of variability. The largest instruments, like the Washington and 

 the Lick glasses, have shown perhaps a dozen other stars appar- 

 ently connected with the nebula. Three of these, seen at Mount 

 Hamilton, are within the inclosure of the ring. A beautiful spark- 

 ling effect which the nebula presents was once thought to be an 

 indication that it was really composed of a circle of stars, but 

 the spectroscope shows that its constitution is gaseous. 



Not far away we find a difficult double star, 17, whose com- 

 ponents are of magnitudes six and ten or eleven, distance 3'7", 

 p. 325. 



From Lyra we pass to Cygnus, which, lying in one of the 

 richest parts of the Milky Way, is a very interesting constella- 

 tion for the possessor of a telescope. Its general outlines are 

 plainly marked for the naked eye by the figure of a cross more 

 than twenty degrees in length lying along the axis of the Milky 

 Way. The foot of the cross is indicated by the star /?, also known 

 as Albireo, one of the most charming of all the double stars. The 

 three-inch amply suffices to reveal the beauty of this object, 

 whose components present as sharp a contrast of light yellow and 

 deep blue as it would be possible to produce artificially with the 

 purest pigments. The magnitudes are three and seven, distance 

 34'6", p. 55. No motion has been detected indicating that these 

 stars are connected in orbital revolution, yet no one can look at 

 them without feeling that they are intimately related to one 

 another. It is a sight to which one returns again and again, al- 

 ways with undiminished pleasure. The most inexperienced ob- 

 server admires its beauty, and after an hour spent with doubtful 

 results in trying to interest a tyro in double stars it is always with 

 a sense of assured success that one turns the telescope to /3 Cygni. 



Following up the beam of the imaginary cross along the cur- 

 rent of the Milky Way, every square degree of which is here worth 

 long gazing into, we come to a pair of stars which contend for the 

 name-letter x- On our map the letter is attached to the southern- 

 most of the two, a variable of long period four hundred and six 

 days whose changes of brilliance lie between magnitudes four 

 and thirteen, but which exhibits much irregularity in its maxima. 

 The other star, not named but easily recognized in the map, is 

 sometimes called 17. It is an attractive double whose colors 

 faintly reproduce those of yS. The magnitudes are five and eight, 

 distance 26", p. 73. Where the two arms of the cross meet is y, 

 whose remarkable cortege of small stars running in curved 

 streams should not be missed. Use the lowest magnifying power. 



At the extremity of the western arm of the cross is 8, a close 



