218 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1953 



Wilson that the spectral absorption lines of distant nebulae show a 

 shift toward the red. The most obvious explanation of this shift is 

 that it is caused by a recession of the nebulae in the line of sight, and 

 Hubble found that the calculated velocities of recession were propor- 

 tional to the distance of the nebulae. By 1948 the velocities of more 

 than 500 nebulae were known, and even at distances of 200 million 

 light-years, which is the limit of the 100-inch telescope for spectra, 

 the velocity computed from the red shift was found to be proportional 

 to the distance. One of the points of chief interest in the application 

 of the 200-inch Hale telescope was to see whether the relation between 

 the velocity and the distance would hold for even more distant nebu- 

 lae than those of which the spectra could be photographed with the 

 100-inch. 



Using the Hale telescope with a short-focus spectrograph at the 

 principal focus, M. Humason has photographed the spectra of a 

 cluster of nebulae in Hydra. The shift of the H and K lines of cal- 

 cium indicates a recession of 37,500 miles a second, and the displace- 

 ment is so great that the lines fall in the blue-green near the long 

 wavelength limit of sensitivity of the undyed IIa-0 emulsion used. 

 Recently Baade published evidence for a revision of the distance 

 scale of the distant stellar systems, as a result of which the nebulae 

 may have to be assigned distances twice as great as those which have 

 heretofore been used and the time scale will be doubled. This change 

 in the scale and the application of the Hale telescope with its powerful 

 auxiliary equipment may make possible some clearer picture of the 

 nature of the red shift. 



Advance in the study of the univei^e is dependent on the collabora- 

 tion of three different branches of science, all of them employed 

 finally by the skilled astronomer, whose results must be analyzed by 

 the mathematician. The optician is making great strides in the devel- 

 opment of new telescopes and new spectroscopes; the chemist is mak- 

 ing the new sensitizing compounds derived from ever more complex 

 organic bases ; and the photographer must make improved emulsions 

 and applj'^ to them the sensitizing dyes, so that he can place in the 

 hands of the astronomer photographic materials worthy of the instru- 

 ments and tlie skill that the astronomer employs. Fortunately, we 

 all are working in harmony and, as the results that I have put before 

 you in this paper show, we are making progress. 



