ASTRONOMY. 283 



stars, and this plan has been devised to bring this interesting branch 

 of astronomy to the attention of observers generally, and to secure de- 

 sirable and needed co-oi^eration in it. The work is easy but very useful, 

 and the plan is so minutely developed as to offer a delightful field of 

 study to amateurs for observation with the naked eye, the common 

 opera-glass, or the small telescope. Correspondence is desired with any 

 persons who wish to undertake this work. 



Mr. G. Knott, writing from Cuckfleld on May 29, states that he had 

 caught a maximum of the apparently capricious variable star '' TJ Gem- 

 inorum^' on May 27 or 28; on both nights it was about 9™ 9. This, 

 compared with the i)revious maximum noted by the same observer on 

 February 28, gives a period of eighty-eight days. 



Professor Schoenfeld finds that a star E. A. IG^^ 13™ 36^, Decl. — 7^ 

 21'.0 for 1855 is variable. 



A star in E. A 19^' 11"^ 33^, Decl. — 2lo 32'.3 for 1850, must be vari- 

 able to a great extent — 0.5 to 9.0 at least. 



Mr. S. 0. Chandler has made the very interesting discovery that the 

 period of the star, D. M. -f 1°, No. 3408, is not 5| days as was at first 

 supposed, but considerably less than one day, viz, 20^ 7™ 4P. 6. The 

 error arose from the star having been visible for some time only in the 

 early evening. The minimum could therefore only be observed at in- 

 tervals of 5.03 days, i. e., G periods, or sometimes 5.87 days, i. e., 7 periods. 

 A combination of these resulted in the period assigned. All the varia- 

 tions from nmximum to minimum, and back to maximum, are accom- 

 l)lislied in about four hours, the maximum brightness being maintained 

 for sixteen hours. This star therefore has the shortest period known, 

 and is the most remarkable for the rapidity of its changes. Tlie dura- 

 tion of increase and of decrease appears to be exactly equal, and the 

 range is about seven-tenths of a magnitude, from G.O or G.l to G.7 or G.8. 



The starD. M +8°, 4890, was observed by I>r. Krueger (1853, August 

 29) as 9.5 magnitude and by Dr. Schoenfeld (1854, September 20) as 9.5 

 magnitude, and it was not seen by Schoenfeld in a zone observed 1854, 

 Sei)tember IG. Dr. de Ball calls attention to the fact that, on August 13, 

 1882, it was barely visible in the eleven-inch refractor of the Bothkamp 

 Observatory. 



In a recent paper presented to the Saint Petersburg Academy of 

 Sciences, Dr. Lindemann.of Pulkova, has investigated the efiect of the 

 red colors of stars on esLimates of their magnitudes. His observations 

 have been made with a Zoellner^s photometer, and he has compared 

 the results of Eosen and Wolff with his own. This is not the place to 

 indicatehis methods, which indeed are laid down in Zoellner's well-known 

 work; but we may quote his general conclusion , to the effect that in 

 matching an artificial star produced by the photometer, with a red star, 

 the accidental errors are very great compared to similar comparisons 

 with white stars, and that in general the sensibility of the eye to red 

 rays is three or four times less than to blue. The errors may amount to 



