MOUNT WILSON OBSERVATORY. 229 



short-period Cepheids, some of which undergo marked light variations 

 in a few hours (p. 266). 



The velocity in space of blue and yellow light, as shown by Mr. 

 Shapley's comparative study of certain variable stars, seems to differ 

 less than one part in a billion (p. 265). 



Hugo Benioff has made preliminary tests on stars of a thalofide cell, 

 with direct-current audion amplifier. The following deflections were 

 observed with the 60-inch reflector: /3 Pegasi (vis. mag. 2.2 to 2.7, 

 type Ma), 52 mm.; Pegasi (vis. mag. 5.2, type Ma), 4 mm; a Andro- 

 medse (vis. mag. 2.2, type AOp), 5 mm. The deflections seemed to be 

 reliable, and the work is being continued with the expectation of 

 reaching fainter stars (p. 266). 



Aided by a new stereocomparator, built in our instrument shop for 

 differential measures of high precision, Mr. van Maanen has continued 

 his trigonometric determinations of parallaxes and proper motions. 

 The total number of parallaxes completed to date is 144. New meas- 

 ures of the parallaxes of five long-period variables, combined with a 

 previously known value for o Ceti, give mean absolute magnitudes of 

 + 1.5 and +6.5 at maximum and minimum, respectively. Theories 

 of variability must therefore recognize the giant character of such stars 

 at maximum (p. 258). A negative parallax was derived for the vari- 

 able nebula N. G. C. 2261, in harmony with Mr. Bubble's view that 

 its rapid apparent changes must be due to progressive variations of 

 illumination rather than actual motion of matter (p. 252). 



Some of the most important of the stellar spectroscopic results of 

 the year have already been mentioned, but much more has been 

 accomplished in this vigorous and successful branch of the Observa- 

 tory's work. The radial velocities of 253 stars have been measured by 

 Messrs. Adams and Joy and Miss Burwell and Miss Brayton. Twenty 

 spectroscopic binaries have been discovered, and the elements of the 

 orbits of 8 spectroscopic binaries have been completed, 7 by Mr. 

 Sanford and 1 by Mr. Duncan (p. 269). 



Much attention has been devoted to variable stars of various types. 

 Ten cluster variables give values from +70 to —180 km. for the "ve- 

 locity of the system," without apparent relationship with distance 

 from the Galaxy. Mr. Joy has determined the orbit of the variable 

 S Antliae which proves to be of the Algol type. The orbit of the 

 Cepheid variable X Cygni has been investigated by Mr. Duncan on 

 the basis of the binary hypothesis. The dark and bright lines of the 

 Cepheid variable W Virginis show marked differences in the radial 

 velocities (p. 268). Remarkable changes in the spectrum of o Ceti 

 were observed near minimum, including a curious asymmetry of the 

 hydrogen lines, such as would result from an angular separation of 

 0''2 in the sources producing them. Peculiar changes were observed 

 in the spectrum of R Scuti. Eight long-period variables with Cepheid 



