258 CARNEGIE INSTITUTION OF WASHINGTON. 



2. Two new variable stars were discovered in the Trifid nebula. 



3. A variable star in M 33, discovered in the summer of 1920, was 

 found to be redder than its neighbors and probably of long period. 



4. Two stars of noticeable proper motion were discovered in the 

 globular cluster M 15. 



5. Lampland's discovery of changes in the Crab nebula (M 1) was 

 confirmed by comparison of a plate made with the 60-inch telescope 

 by Ritchey in 1910 with one made by Duncan in 1921 ; the motions of 

 12 nebulous condensations with respect to 13 comparison stars were 

 measured. The displacement of the nebulous points was in general 

 away from the center of the nebula. The maximum displacement in 

 the 11| years interval was about 2 ''5. 



6. The evidence afforded by comparing the photographs of M 9^ 

 with two plates taken by Mr. Seares in 1916 is insufficient either to 

 confirm or disprove the changes announced by Lampland. 



MISCELLANEOUS PHOTOGRAPHS. 



A few photographs of the moon, Jupiter, Saturn, and Venus have 

 been made by Mr. Pease with the 100-inch telescope. 



Photographic observations of the positions of the Eighth and Ninth 

 Satellites of Jupiter were made by Mr. Nicholson with the 60-incb 

 telescope. No ephemeris for either satellite was available. Approxi- 

 mate positions were computed and the satellites searched for until 

 found. 



TRIGONOMETRIC PARALLAXES AND PROPER MOTIONS. 



During the year Mr. van Maanen has secured 370 plates at the 80- 

 foot focus of the 60-inch reflector with 614 exposures. Of these, 

 455 exposures were for the determination of parallaxes, 139 for proper 

 motions, and 20 for photometric determinations. For 22 fields the 

 necessary plates were secured for the determination of parallaxes, 

 thus giving a total of 144 fields finished to date. Several of the results 

 require comment. 



a. Parallaxes were derived for 5 long-period variables: T Cassiopeiae, 

 R Trianguli, R Virginis, R Canum Venaticorum, and X Ophiuchi. 

 Including, also, the parallax of o Ceti determined by other observers, 

 mean absolute magnitudes for these objects were found to be as fol- 

 lows: maximum about +1-5; minimum -|-6.5; at maximum these stars 

 are therefore giants. Any theory of their variability must keep this 

 fact in view. 



6. For two Cepheids, RX Aurigse and RR Lyrse, the parallaxes 

 found are — 0''001 and +0''006, respectively, thus confirming pre- 

 vious determinations of the absolute brightness of stars of this type. 



c. The parallax found for R Monocerotis (N. G. C. 2261), the well- 

 known variable nebula, is negative. The true parallax must therefore 

 be very small, probably less than -t-0''005. To explain the extraordi- 



