202 CARNEGIE INSTITUTION OF WASHINGTON. 



counts of 40,000 stars, a reliable measure of the relation between stellar 

 density and galactic latitude has been deduced which is in harmony 

 with Professor Kapteyn's conclusion that the faint stars show a high 

 galactic condensation. This result is further confirmed by a discussion 

 of Professor Turner's counts of some 600,000 stars in the Astrographic 

 Catalogue. Stars of photographic magnitude 17.5 are from twenty to 

 thirty times as numerous in the plane of the Milky Way as at its poles. 



The continuation of a comprehensive investigation of globular star 

 clusters has jdelded new and interesting results. Thus it appears to 

 be possible to estimate the relative distances of clusters containing 

 typical short-period variable stars, since the median magnitudes of 

 these objects are constant for each cluster, while varying from one 

 system to another. The method, if substantiated by further work, will 

 be of great value, in view of the extreme remoteness of these objects, 

 which places them beyond the reach of other means of measuring 

 distances. 



Another outcome of this investigation is the discovery that the distri- 

 bution of the fainter stars in certain globular clusters reveals an appar- 

 ently characteristic elliptical form. In Messier 13, for example, there 

 is an axis of elongation along which the stai-s are 30 per cent more 

 numerous than along the minor axis. As this result is supported by 

 other phenomena, it may prove that the so-called globular clusters are 

 actually more or less flattened spheroids, analogous to our own galactic 

 system. Additional work on clusters shows no evidence of effectual 

 scattering of light in space and indicates provisionally that the depth 

 of the Milky Way in some directions may exceed 25,000 Ught-years. 



The Observatory's policy of devoting special attention to laboratory 

 investigations for the interpretation of solar and stellar phenomena 

 has been continued with the aid of improved faciUties. The electric 

 furnace has been used for the study of anomalous dispersion phenom- 

 ena and for the investigation of the effect of changes in temperature, 

 vapor density, and surrounding atmosphere on the spectra of iron, 

 calcium, strontium, and barium. The very diffuse arc lines of barium 

 are sharp and of modified structure in the furnace, where a triplet or 

 doublet sometimes appears in the place of the single arc Une. Measure- 

 ments of the sharp furnace lines indicate their apparent agreement with 

 faint unidentified lines of the solar spectrum, where their structure 

 corresponds with that given by the furnace. The series lines of cal- 

 cium, produced by the impact of cathode rays, show marked differences 

 of intensity as compared with their appearance in other sources. 



The further study of the effect of an electric field on radiation, which 

 has now been extended to include the spectra of iron, chromium, nickel, 

 titanium, and manganese, has shown no appreciable effect for the 

 great majority of lines; 74 lines of chromium, 8 of iron, and about 



