95 " RECORDS 



telescope tube cannot be used. The image of another star 

 just outside of the photographic plate is made use of. By means 

 of a little eye-piece with a fine pair of cross hairs, attached to 

 the plate holder which is adjustable in two directions at right 

 angles to each other, the image of the guide star is kept on the 

 intersection of the cross-hairs during the entire time of exposure. 

 The photographs taken at the Yerkes Observatory in this man- 

 ner by Mr. Ritchie are much finer than those taken at Potsdam 

 with a photographic telescope. 



A most important application of photography with this tele- 

 scope will be the determination of the parallax of stars, which 

 has not yet deen done to any extent by photographic means. 



Photographs of small planetary nebulae taken with this tele- 

 scope show more than can actually be seen with our eyes, in 

 some cases for example, a radial structure. 



The instrument can also be used to study stellar spectra and 

 stellar evolution. We can pass by gradations from the types of 

 hot and white stars like Sirius, to the more developed and colder 

 ones like our sun, and then to the red stars. There are two 

 types of red stars and by the aid of their spectra photographed 

 with this telescope we have detected a relationship between the 

 two types, through the presence of carbon bands. Even in the 

 atmosphere of the sun there is a very thin layer of carbon vapor 

 and above this the gases of the chromosphere. In the red stars 

 we have this carbon vapor, which is very dense in one of the 

 types. 



Another important line of work is that of measuring the mo- 

 tion of stars in the line of sight. Professor Frost uses the tita- 

 nium line for this purpose, and has just had a new spectrograph 

 constructed for the work. 



In photographing the spectrum of Saturn with its rings, we 

 find a faint band in the red, indicating the presence of a com- 

 paratively dense absorbing atmosphere on the planet which is 

 absent from the rings. 



With the help of a spectroheliograph, we are able to photo- 

 graph solar phenomena. These photographs show that the 

 mottling of the sun's surface persists throughout the minimum 



