REPORT OF COMMITTEE ON OBSERVATORIES 65 



give reliable information as to their physical condition and state of 

 development. The secular changes of any star are so slow that 

 thousands of years might be required to detect them. But it fortu- 

 nately happens that all stages of growth are now represented. It 

 is as though one were to pass through an oak forest and seek to 

 learn of the development of the trees. During the period of his stay 

 no apparent change would occur. But he would have before him 

 trees of the same species in every stage of growth : the acorn, the 

 sapling, the oak in its prime, and the dying tree, representing the 

 last stage in the evolutional process. By observing these, the evolu- 

 tion of a single tree could be understood. Thus in the stars, while 

 their changes are too slow to be observed, a similar opportunity 

 exists of tracing their life history. Preceding the condition of the 

 sun we find stars like many of those in the constellation Orion, 

 which have advanced but little beyond the state of nebulae. Next 

 to these come white stars like Sirius, which are but slightly con- 

 densed, and represent what the sun must have been millions of years 

 ago. From these it is possible to pass by gradual steps through the 

 process of development which leads to the production of yellow 

 stars like the sun. Here the process of decline has apparently set 

 in, and the beginnings of the last stage are faintly visible. Finally 

 come the orange and red stars, the spectra of which reveal phe- 

 nomena of the greatest interest, such as the sun will exhibit after 

 the lapse of many centuries. 



Existing instruments have sufficed to develop the main lines in 

 this process of evolution, but there are numberless questions which 

 cannot be answered without the aid of much more powerful tele- 

 scopes. A great reflector, such as would be most suitable for photo- 

 graphing the nebulae, would also be much superior to any existing 

 telescope for the spectroscopic investigations which furnish the data 

 required in this research. Reference has already been made to 

 the possible existence of great sun spots on the red stars ; these 

 and many similar questions of equal importance in connection with 

 the constitution of the sun cannot be solved until such instrumental 

 means have been provided. 



Throughout all of this work, both on the sun and the stars, it 

 would be necessary to have constant recourse to laboratory experi- 

 ments in order to interpret the observed phenomena. A suitable 

 equipment of physical apparatus for this purpose is therefore essen- 

 tial in connection with a solar observatory. 



