Page:Popular Science Monthly Volume 47.djvu/218

208 1·6″, 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 36″, p. 170°; Σ 2654, magnitudes six and eight, distance 12″, p. 234°; Σ 2644, magnitudes six and seven, distance 3·6″, p. 208°.

The star η is an interesting variable between magnitudes three and a half and 4·7; period, seven days, four hours, fourteen minutes. 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 ranging from the ninth down to the twelfth magnitude.

Just north of Aquila is the little constellation Sagitta, containing several interesting doubles and many fine star fields, which may be discovered by sweeping over it with a low-power eyepiece. The star ζ 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 θ we find three components of magnitudes seven, nine, and eight respectively, distances 11·4″, p. 327°, and 70″, p. 227°. A wide double is ε, magnitudes six and eight, distance 92″, p. 81°. Nebula No. 4572 is planetary.

Turning to Delphinus, we find a very beautiful double in γ, magnitudes four and five, distance 11″, p. 273°, colors golden and emerald. The leader α, which is not as bright as its neighbor β, 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°, β 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.

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° C. 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.