THE PROGRESS OF SCIENCE. 



379 



CCELOSTAT AND SECOND MIRROR OF NEW TELESCOPE. 



provisional site, and $10,000 was ap- 

 propriated for a thorough trial of the 

 mountain. Later the institution de- 

 cided to undertake the construction 

 and equipment of a solar observatory 

 at this point and up to the present 

 time has devoted more than $300,000 

 for the purpose. Professor George E. 

 Hale, former director of the Yerkes 

 Observatory, has been made permanent 

 director, and under his care the in- 

 stallation of the observatory has gone 

 forward with characteristic energy. 

 At the present time the Snow horizon- 

 tal telescope and various buildings 

 necessary for the proper execution of 

 the work of such an observatory are 

 Hearing completion. The program of 

 work which Professor Hale has laid 

 out, in a very condenseu form, is as 

 follows : 



The ends sought are two : 



(1) The Study of the Sun as a Typical Star. 



(2) The Study of the Sun as the Center of the 



Solar System. 

 The investigations include : 

 I. Direct photography. 



(a) Daily photographs of the Sun on a Scale 

 of 6.7 inches. 



(b) Large scale photographs of spots nnd 

 other regions. 



II. Photographic Studies of the Solar Atmos- 

 phere with the Spectroheliograph, 



(a) Daily photographs of the Sun taken 

 with H„ H 2 , and HS, and other dark 

 lines for calcium flocculi and promi- 

 nences. 



(6) Measurement and discussion of the 

 photographs. 



III. Spectroscopic Investigations. 



(a) Daily photographs of spectra of spots. 

 (6) A study of velocity of motion of flocculi 

 and prominences. 



(c) Bolometric measurements of relative 

 radiation of sun-spots, faculce, and pho- 

 tosphere. 



(d) Spectroscopic measurement of solar ro- 

 tation. 



IV. Studies of total solar radiation. 



V. Comparative laboratory investigations. 



The Snow horizontal telescope is 

 provided with two concave mirrors, one 

 of GO feet focus, and the other of 145 

 feet focus, either of which can be used 

 as desired. The beam of sunlight falls 

 first upon a plane mirror of 30 inches 

 diameter, whence it is reflected to a 

 second plane mirror of 24 inches diam- 

 eter, which sends it to the concave mir- 

 ror of the telescope. With the image 

 thus obtained any of the pieces of work 

 outlined above may be carried out. 



The spectroheliograph is the creation, 

 in large part, of Professor Hale him- 

 self, in whose hands it has led to re- 

 markable results. The principles in- 

 volved seem to have been suggested first 



