equipment. Its mode of attack and its means of 

 progress must grow with its work and develop 

 with the disclosure of new and unexpected possi- 

 bilities. 



ADVANTAGES OF A MOUNTAIN SITE. 



It was New T ton who first pointed out the impor- 

 tance of making astronomical observations from a 

 mountain top: "For the Air through which we 

 look upon the Stars, is in a perpetual Tremor; as 

 may be seen by the tremulous Motion of Shadows 

 cast from high Towers, and by the twinkling of the 

 fix'd stars. . . . The only remedy is a most 

 serene and quiet Air, such as may perhaps be 

 found on the tops of the highest Mountains above 

 the grosser Clouds." (Opticks, third edition, p. 98.) 



But height is not the only essential; indeed, very 

 great altitudes are to be avoided. The summit of 

 the Rocky Mountains is a notoriously bad place 

 for astronomical work, because of the unstable 

 atmospheric conditions and the frequent storms. 

 Long periods of unbroken weather, free from rain 

 and with little cloud, are associated with that 

 tranquillity and steadinessof the atmospherewhich 

 Newton so much desired. These are to be found 

 on the mountains of the Sierra Madre range, in 

 the semi-tropical climate of Southern California. 

 Mount Wilson, selected by Hussey after many 

 tests of other elevated points in the northern and 

 southern hemispheres, was accordingly chosen as 

 the observation station. Rising abruptly from 



