338 SMITHSONIAN MISCEIvLANEOUS COLIvECTlONS VOL. 52 



endless succession of mountains tributary to the high Sierras, and 

 on the south to the Mexican frontier. In the San Gabriel Valley, 

 lying at the base of Mount Wilson, and about eight miles distant 

 in an air line, is the city of Pasadena. Here a large part of the ob- 

 servatory work, such as various laboratory investigations, the design 

 and construction of instruments, and the measurement and discus- 

 sion of astronomical photographs taken on the mountain, is con- 

 ducted. By confining the work on Mount Wilson almost entirely to 

 observations, the expense of maintaining the rest of the establish- 

 ment there is avoided and many other advantages are secured. 



In enumerating the various opportunities which- lay open to the 

 Solar Observatory at the time of its inception, the possibility of 

 bringing into use large and powerful spectroscopes, which had been 

 developed in physical laboratories, was first mentioned. In 1859 

 Kirchhofif discovered with the spectroscope the chemical composi- 

 tion of the Sun, and proved that this instrument is capable of 

 analyzing the light which reaches us from any luminous source. 

 When applied later to a study of the phenomena of the Sun and 

 stars, the spectroscope, then of small dimensions, was simply at- 

 tached to the end of a telescope tube. The invention of the concave 

 grating by Rowland in 1882, and the widespread use of this powerful 

 instrument in physical laboratories, introduced a new era, through 

 the great increase in precision of measurement rendered possible by 

 its high dispersion. In astronomy, however, the equatorial refractor 

 continued to be the popular form of telescope, and the spectroscope, 

 though improved in many particulars, did not increase greatly in size. 

 It was obviously impossible to attach a concave grating spectro- 

 scope over 21 feet in length to the end of a moving telescope tube. 

 Consequently the precision of measurement in astronomical spectro- 

 scopy has been far inferior to that attained in the laboratory. 



The Snow Telescope 



At the period when the plans for the Solar Observatory were 

 taking form, the principles which should govern the construction of 

 a fixed telescope were partly understood, and had been frequently 

 applied in eclipse observations. Almost simultaneously with our 

 experiments with fixed telescopes at the Yerkes Observatory, a large 

 instrument of this type, giving a solar image well suited for bolo- 

 metric work, was constructed for the Smithsonian .\strophysical 

 Observatory. Such telescopes, however, had not been used for re- 

 searches demanding a large and sharply defined solar image. The 

 Snow telescope, constructed in the instrument shop of the Yerkes 



