226 CARNEGIE INSTITUTION OF WASHINGTON. 



by Mr. Gingrich and Mrs. Marsh and a total of 22 have now been finished. 

 Some of the results of the year may be indicated in a brief summary : 



(1) Among the objects for which parallaxes have been derived are two 

 short-period variables, U Ophiuchi and UU Herculis; two long-period variables, 

 R Cancri and U Herculis; and five planetary nebulae, N. G. C. 1501, 1514, 

 6058, 6572, and 7226. 



(2) A faint companion, magnitude 11.8, has been found by Mr. van Maanen 

 12' southeast of Lalande 32324. Its proper motion, as determined by Mr. 

 Gingrich, is 0''575 in position angle 156°, while that of the principal star is 

 0''56 in position angle 153°. Assuming the stars to have the same parallax, 

 the fainter star has an absolute magnitude of +11.2, and its distance from the 

 primary is 10,000 astronomical units. 



(3) The measurement and reduction of a series of plates of X Ophiuchi by 

 Mr. Gingrich shows that the displacement in the image of this close double 

 star is due to the variability of the northern component, and that the distance 

 is somewhat more than 0'' 152. These conclusions are in agreement with those 

 of Mr. van Biesbroeck, of the Yerkes Observatory, from visual observations. 



(4) Mr. van Maanen has made a new discussion of the systematic errors 

 of the Mount Wilson trigonometric parallaxes, using several methods, based 

 for the most part on objects whose parallaxes are known within a few thou- 

 sandths of a second of arc from sources other than direct measurement. 

 Among these are stars of types O, B, and N; short-period variables, long- 

 period variables, and spiral nebulae. From 8 different comparisons it is 

 found that the systematic error in the trigonometric parallaxes is — 0''0024 

 =*=0 ''0003. In view of the possibility that the parallaxes of some objects 

 with very high color-indices, such as the planetary nebulae, may be affected 

 with considerably larger systematic errors, a series of photographs of these 

 objects has been begun at both the primary and the 80-foot focus of the 60- 

 inch reflector. The measurement of the proper motions from these plates 

 will make it possible to derive mean parallaxes from parallactic motion and the 

 r-component. 



(5) The parallaxes and the proper motions in right ascension of 20 stars 

 in the nebulous region surrounding the star B. D. +31° 643 near o Persei have 

 been determined by Mr. Gingrich. The mean of the parallaxes of the five 

 stars most completely surrounded by nebulosity is +0''0095. If this is taken 

 as the parallax of the nebula, its distance is about 350 light-years. 



At the primary focus of the 100-inch reflector Mr. van Maanen has made 

 224 photographs with 408 exposures. Plates have been taken as far south 

 as 7 Sagittarii, 8= — 36°47', through a yellow color-screen made by Mr. 

 Anderson, and show good images. This screen is being used for all fields 

 south of —4°. The parallax of one eleventh-magnitude star, Wolf 1039, 

 with a total proper motion of 1*44, has been determined from these plates. 

 The result is 7r re i= +0?056 ±0?004. 



STELLAR PHOTOMETRY. 



The photographs relating to investigations in stellar photometry have been 

 taken by Messrs. Seares, Hubble, and Humason. 



The observations of colors of stars in the Selected Areas of the 30° zone 

 referred to in the last report are well advanced. All but three of the twenty- 



