742 THE POPULAR SCIENCE MONTHLY. 



constellation Virgo, is roughly outlined by the stars ^, -q, y, 8, and 

 c, which form two sides of a square some 15 across. It extends, 

 however, for some distance into Coma Berenices, while outlying 

 nebulae belonging to it are also to be found in the eastern part of 

 Leo. Unfortunately for those who expect only brilliant revela- 

 tions when they look through a telescope, this throng of nebulsa 

 consists of small and inconspicuous wisps as ill defined as bits of 

 thistle-down floating high in the air. There are more than three 

 hundred of them all told, but even the brightest are faint objects 

 when seen with the largest of our telescopes. Why do they con- 

 gregate thus ? That is the question which lends an interest to 

 the assemblage that no individual member of it could alone com- 

 mand. It is a mystery, but beyond question it is explicable. The 

 explanation, however, is yet to be discovered. 



The places of only three of the nebulae are indicated on the 

 map. No. 2806 has been described as resembling in shape a shut- 

 tle. Its length is nearly one third of the moon's diameter. It is 

 brightest near the center, and has several faint companions. No. 

 2961 is round, 4' in diameter, and is accompanied by another round 

 nebula in the same field of view toward the south. No. 3105 is 

 double, and powerful telescopes show two more ghostly compan- 

 ions. There is an opportunity for good and useful work in a care- 

 ful study of the little nebulae that swim into view all over this 

 part of Virgo. Celestial photography has triumphs in store for 

 itself here. 



Scattered over and around the region where the nebulae are 

 thickest we find eight or nine variable stars, three of the most 

 remarkable of which, R, S, and U, may be found on the map. R 

 is very irregular, sometimes attaining magnitude six and a half, 

 while at other times its maximum brightness does not exceed that 

 of an eighth-magnitude star. At minimuin it sinks to the tenth 

 or eleventh magnitude. Its period is one hundred and forty-five 

 days. U varies from magnitude seven or eight down to magni- 

 tude twelve or under and then regains its light, in a period of 

 about two hundred and seven days. S is interesting for its bril- 

 liant red color. When brightest, it exceeds the sixth magnitude, 

 but at some of its maxima the magnitude is hardly greater than 

 the eighth. At minimum it goes below the twelfth magnitude. 

 Period, three hundred and seventy-six days. 



Next east of Virgo is Libra, which contains a few notable 

 objects (map No. 10). The star a has a fifth-magnitude compan- 

 ion, distant about 2'M)", which can be easily seen with an opera 

 glass. At the point marked A on the map is a curious multiple 

 star, sometimes referred to by its number in Piazzi's catalogues 

 as follows: 212 P. xiv. The two principal stars are easily seen, 

 their magnitudes being six and seven and a half; distance 15", p. 



