158 CARNEGIE INSTITUTION OF WASHINGTON. 



After a brief statement regarding the conditions found at Mount 

 Wilson had been presented to the Executive Committee of the 

 Carnegie Institution, in April, 1904, they decided to make a grant 

 of a sum sufficient to provide for the erection and use of the Snow- 

 telescope on the mountain. The Yerkes Observatory loaned the 

 telescope and the University of Chicago provided the salaries of 

 some of the observers. The work accomplished on the mountain 

 since this grant was made has been sufficient to serve as a reliable 

 basis for estimates on the cost of a large solar observatory, besides 

 giving valuable experience regarding the necessary methods and 

 cost of construction under the unusual conditions existing at the 

 summit of a mountain nearly 6,000 feet in height. In view of their 

 bearing on the question of a solar observatory, I have accordingly 

 included in my report some remarks on the principal obstacles 

 encountered and overcome in the construction of buildings and the 

 transportation of instruments and materials. 



REQUIREMENTS OF A SITE FOR A SOLAR OBSERVATORY. 



It is desirable to recapitulate here the purposes and plans for a 

 solar observatory whjch were given at some length in Year Book 

 No. 2 of the Carnegie Institution. At the outset, it should be stated 

 that the term "solar observatory" is used here in a broad sense, 

 since it is not intended to exclude from the program certain investi- 

 gations of stars which are of fundamental importance in any 

 general study of the problem of stellar evolution. For the sun is 

 a star, comparable in almost every respect with many other stars 

 in the heavens, and rendering possible, through an intimate know- 

 ledge of its own phenomena, the solution of some of the most 

 puzzling questions in the general problem of stellar evolution. 

 Conversely, however, 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 

 instruments especially designed for the study of stellar problems. 



The plan of work proposed for the observatory, as outlined in 

 Year Book No. 2, includes the following classes of observations : 



(i) Frequent measurements of the heat radiation of the sun, to 

 determine whether there may be changes during the sun-spot cycle in 

 the amoimt of heat received from the sun by the earth and in the 

 relative radiation of the various portions of the solar surface. 



