164 REPORTS ON INVESTIGATIONS AND PROJECTS. 



(5) The continuation by two different methods of the study of the possi- 

 biHty of determining photometric magnitudes with the 60-inch reflector by 

 the use of diaphragms over the mirror indicates that over a range of 5 mag- 

 nitudes the effect of the change in the diffraction pattern produced by 

 reducing the aperture is practically negligible. 



(6) The same investigation shows, however, that the correction to the 

 observed magnitudes depending on the distances of the stars from the center 

 of the plate is very large and variable from plate to plate. The correction is 

 dependent upon the size of the photographic star-image, but is independent 

 of the color of the star and of the various factors entering into the develop- 

 ment of the photographic plate. 



(7) About 600 photographs of the spectra of nearly 200 stars between the 

 fifth and seventh magnitude have been obtained since December with the 

 60-inch reflector, at the secondary focus of 80 feet. Of these, 50 are of the 

 solar type of spectrum and the remainder are of types A and B. The spectra 

 have been employed both for purposes of classification and for determina- 

 tions of radial velocity. Over 50 spectroscopic binaries have been discovered 

 during the measurement of the photographs. 



(8) Photographs of the spectra of three globular star-clusters confirm 

 the result found in 1910 from nine clusters, that these objects have in general 

 a spectrum of the F type. One spiral nebula has been found giving a spec- 

 trum of the K type ; all others that have been investigated show spectra of 

 the G type. 



(9) A continuation of the statistical study of the motions of stars of the 

 Orion type of spectrum leads to a modification of the vievv^ that the Perseus 

 and Scorpius-Centaurus groups represent two great star-streams among the 

 Orion stars. It now appears probable that they form a part of a single 

 stream to which all known Orion type stars must belong. The existence of 

 the two-stream motion for stars of the solar type and type A, but not for the 

 Orion type stars, may find an explanation in the hypothesis that the number 

 of stars belonging to the second stream is a function of the spectral type, and 

 decreases steadily from the solar type through type A to the Orion type. 



(10) A study of the Zeeman effect for about 1,120 lines in the spark 

 spectrum of iron and titanium has given the following results: 



(a) The relationship of the measured separations to the normal interval 

 agrees closely with Runge's law. 



(b) Groups of lines of the same type of resolution are found among the 

 more complex types for which the similarity of the intervals between the 

 components indicates an intimate relationship. 



(c) The law that the mean separation is proportional to the square of the 

 wave-length is found to hold closely for the average of the lines taken in 

 successive intervals throughout the wide range of wave-length covered by 

 the observations. 



