MOUNT WILSON OBSERVATORY. 259 



nary changes in the nebula observed by Mr. Hubble, it seems necessary 

 to conclude that the necessary motions are an effect of illumination 

 and do not represent a real motion of nebulous matter. 



d. A parallax of +0''10 was derived for the faint star of magnitude 

 13.2, proper motion 0''38, discovered by Mr. van Maanen while meas- 

 uring the parallax of Boss 1182. This indicates an absolute magni- 

 tude of +8.2 and a velocity at right angles to the line of sight of about 

 180 km. per sec. 



A series of parallax plates has been started at the 42-foot focus of 

 the 100-inch reflector; the program includes objects which are too 

 faint or too far south to be dealt with at the 80-foot focus of the 60-inch 

 telescope. Among these are some of the largest planetary nebulae, 

 a few early novse, and some faint stars of large proper motion. 



Two pairs of plates of 5-years' interval, of the region around 

 a Tauri, have been measured for proper motion. Of 65 stars down to 

 magnitude 15, not one appears to be a member of the Taurus group; 

 the percentage of faint stars belonging to the cluster must therefore 

 be extremely small. 



Mrs. Marsh has assisted in the computations relating to parallax 

 and proper motion and has also measured ten fields for the determina- 

 tion of proper motions of stars of about the twelfth magnitude. For 

 this purpose several plates originally taken for the determination of 

 parallax were duplicated, the interval being five or six years. 



STELLAR PHOTOMETRY. 



Several hundred photographs have been made for photometric 

 purposes with the 10-inch refractor and the reflectors by Messrs. 

 Seares, Shapley, Hubble, Humason, and LindbLad of a variety of 

 objects. Besides the determination of photographic and photo- 

 visual magnitudes in the special fields referred to below, a series of 

 66 photographs of the cluster M 5 has been made, at the request of 

 Professor Turner, by Mr. Seares and Mr. Lindblad, for the determina- 

 tion of the magnitudes of comparison star k of Bailey's variable No. 

 33. Star k is a variable of short period and small amplitude. 



An object of unusual interest, called to our attention by Professor 

 von Zeipel, is a very red star of about the thirteenth photo visual 

 magnitude in the edge of the cluster M 37. The star is a variable of 

 unknown period and amplitude. Its color-index seems to be of the 

 order of five magnitudes. Polar comparisons have been made for the 

 determination of its brightness and color, but ths photographs have 

 not yet been reduced. 



Mr. Hubble has used the 10-inch Cooke refractor to determine by 

 polar comparisons the photovisual magnitudes of 250 stars involved 

 in or neighboring on nebulae and nebulous clusters. Photographic 

 magnitudes have been determined for 160 of these stars. Ordinary 

 photographic magnitudes obtained with this instrument are much 



