ASTRONOMY — HALK. 77 



shops were immediately fitted up and brought into use, and the 

 optical shop, which required special fittings, has been in operation 

 since July. A 24-inch concave mirror of 143 feet focal length and a 

 20-inch plane mirror have been nearly completed, and work on the 

 5-foot mirror is in progress. 



In addition to the large amount of work done in fitting up the 

 shop and making special tools, etc., the following instruments have 

 been nearly or quite completed : 



Spectroheliograph of 8 inches aperture and 60 inches focal length, with several 

 sets of curved slits and various accessories. 



Stellar spectrograph of 5 inches aperture and 13 feet focal length, with con- 

 stant-temperature case and support for large plane grating. 



Solar spectrograph ( Littrow type) of 6 inches aperture and 18 feet focal length.. 



vSpectroheliograph temporarily used with the Snow telescope. 



Electric slow motions for 24-inch concave mirror of Snow telescope. 



Globe-measuring machine for solar photographs. 



Apparatus for removing the mirrors of Snow telescope from their cells when 

 silvering. 



All the patterns for the above work and much special furniture 

 for the offices and laboratories have been made in the pattern shop. 



FIVE-FOOT REFLECTOR. 



The 5-foot mirror, which will form the principal optical part of the 

 largest and most powerful telescope of the Solar Observatory, was 

 brought out from the Yerkes Observatory last spring. It was packed 

 with special precautions, under the personal supervision of Mr. 

 Ritchey, in a double case, supported by two systems of spiral springs. 

 The mirror arrived safely in Pasadena and is now being polished. 

 Detailed drawings for the heavy mounting are being made by our 

 draftsmen, under Mr. Ritchey's direction, and are so far completed 

 . as to enable the Union Iron Works Company of San Francisco to 

 undertake work on the large castings. Several of these are finished 

 and the nickel-steel forging for the polar axis has also been machined. 

 There is every reason to hope that the mounting will carry the mirror 

 with the high degree of precision necessary for the most refined 

 photographic work. 



