ASTRONOMY ON THE PACIFIC COAST 217 



The wise economical policy of this observatory is to engage prin- 

 cipally in those investigations which can not be carried on with smaller 

 and less effective instruments. Much that could be done there is left to 

 smaller institutions. The great instruments are used only for the prob- 

 lems that demand their great power. And these are quite sufficient to 

 keep them in constant use. 



Turning now to the Mount Wilson Solar Observatory we find a 

 unique institution. As its name implies, it is an observatory erected 

 primarily for the study of the sun. 



In 1902, Dr. S. P. Langley addressed a communication to the Carnegie In- 

 stitution recommending the establishment of an observatory at a very high alti- 

 tude for the special purpose of measuring the solar radiation. 



This recommendation resulted ultimately in the erection of the 

 Solar Observatory by the Carnegie Institution by which it is supported. 

 Various sites in Arizona and in southern California were tested, and the 

 summit of Mount Wilson (nearly 6,000 feet above sea-level) near Pasa- 

 dena in southern California was selected. In the choice of a site for 

 this observatory excellent " seeing " conditions in day time as well as at 

 night were of primary importance. Such conditions were found to 

 exist on Mount Wilson. 



For director of the observatory a very wise choice was made in Dr. 

 George E. Hale. It is due principally to his genius and untiring efforts 

 that this wonderful plant has been designed and brought to its present 

 high state. 



Dr. Hale points out that the term " solar observatory " is to be used 

 in a broad sense, 



since it is not intended to exclude from the program certain investigations 

 of stars which are of fundamental importance in any general study of the prob- 

 lem of stellar evolution. For the sun is a star, comparable in almost every re- 

 spect with many other stars in the heavens, and rendering possible, through an 

 intimate knowledge of its own phenomena, the solution of some of the most 

 puzzling questions in the general problem of stellar evolution. Conversely, how- 

 ever, the stars are suns, and if we would know the past and future conditions of 

 the sun, we must examine into the physical condition of stars which represent 

 earlier and later stages of development. It will be seen that there is ample! 

 ground for the inclusion in the equipment of a solar observatory of certain in- 

 struments especially designed for the study of stellar problems. 



Such an observatory, whose primary object is " to apply new instru- 

 ments and methods of research in a study of the physical elements of 

 the problem of stellar evolution," must of necessity have as comple- 

 mentary parts of its equipment a physical laboratory and an adequate 

 machine shop. These two parts have been supplied and are located in 

 Pasadena. Here not only are smaller pieces of apparatus made and 

 repaired, but also the enormous discs of glass for the 60-inch and the 

 100-inch reflectors have been figured and tested. 



The instrumental equipment of the solar observatory is naturally 



