208 THE POPULAR SCIENCE MONTHLY. 



tance I'd", p. 122 ; 23, magnitudes six and ten, distance 3*4", p. 12 

 requires the five-inch and good seeing ; 57, magnitudes five and 

 six, distance 3G", p. 170 ; 2 2654, magnitudes six and eight, dis- 

 tance 12", p. 234 ; 2 2044, magnitudes six and seven, distance 

 3-6", p. 208. 



The star -q is an interesting variable between magnitudes three 

 and a half and 4"7 ; period, seven days, four hours, fourteen min- 

 utes. The small red variable R changes from Magnitude six to 

 magnitude seven and a half and back again in a period of three 

 hundred and fifty-one days. 



Star cluster No. 4440 is a very striking object, its stars rang- 

 ing from the ninth down to the twelfth magnitude. 



Just north of Aquila is the little constellation Sagitta, con- 

 taining several interesting doubles and many fine star fields, 

 which may be discovered by sweeping over it with a low-power 

 eyepiece. The star is double, magnitudes five and nine, distance 

 8*6", p. 312. The larger star is itself double, but far too close to 

 be split, except with very large telescopes. In 9 we find three 

 components of magnitudes seven, nine, and eight respectively, 

 distances 11'4", p. 327, and 70", p. 227. A wide double is e, mag- 

 nitudes six and eight, distance 92", p. 81. Nebula No. 4572 is 

 planetary. 



Turning to Delphinus, we find a very beautiful double in y, 

 magnitudes four and five, distance 11", p. 273, colors golden and 

 emerald. The leader a, which is not as bright as its neighbor (3, 

 and which is believed to be irregularly variable, is of magnitude 

 four, and has a companion of nine and a half magnitude at the 

 distance 35", p. 278. At a similar distance, 35", p. 335, /3 has an 

 eleventh-magnitude companion, and the main star is also double, 

 but excessively close, and much beyond our reach. It is believed 

 to be a swiftly moving binary, whose stars are never separated 

 widely enough to be distinguished with common telescopes. 



In the studies of Raoul Pictet and Altschul on phosphorescence at very low 

 temperatures, glass tubes containing sulphides of calcium, strontium, and barium, 

 exposed to sunlight for periods that were noted, were plunged into liquid nitrous 

 oxide, the temperature of which, by rapid diminution of pressure, could be brought 

 to 140 0. After twelve minutes' immersion the tubes were brought into a 

 dark room and their behavior was carefully observed. At first, no indication of 

 phosphorescence could be observed. In a few moments the upper part of the 

 tube, which had not been so strongly cooled as the rest, began to phosphoresce, 

 and gradually the feeble light seemed to spread itself down the tube, the lower 

 part of which, however, glowed more feebly than the upper. After five minutes 

 the tubes acquired their ordinary vivid color, without subsequent exposure to 

 sunlight or even to diffused daylight. All phosphorescent substances appeared to 

 behave in this way. 



