292 CARNEGIE INSTITUTION OF WASHINGTON. 



lines of the gas in the tube, and it also brings out the enhanced lines 

 of the electrodes. Interesting preliminary results have been obtained 

 for oxygen, nitrogen, and iron. Through the courtesy of Admiral 

 Griffin a quantity of helium has been obtained from the Bureau of 

 Steam Engineering of the U. S. Na\^, and a study of helium, hydro- 

 gen, and perhaps other gases will be undertaken. 



Messrs. Anderson and Babcock have commenced a study of the 

 transmission of the atmosphere for short wave-lengths. The spectrum 

 of an iron arc burning on Mount Wilson is photographed by means of a 

 quartz spectrograph in Pasadena. The air-path lias a length of 7 

 miles and is equivalent to 1.4 atmospheres. The trials so far made 

 have been under poor conditions, due to the prevalence of very thick 

 haze. Nevertheless, X2740 has been recorded with an exposure of one 

 hour, although, as is well known, the solar spectrum ends at X2890. 



The chemical identification of the air-lines in spark spectra in the 

 region X5927 to X8683 have been made more complete by additional 

 experiments involving exposures to the spark in pure oxygen. The 

 photographs were secured by Messrs. Clyde R. Keith and F. L 

 Hopper under the direction of Mr. Merrill. The work confirmed the 

 preliminary results from this laboratory, as well as those obtained by 

 other observers using vacuimi tubes, and added some identifications 

 not previously available, 



CONSTRUCTION DIVISION. 



DRAFTING AND DESIGN. 



The work of drafting and design has covered a wide range, as new 

 instruments and appliances are frequently needed in all branches of the 

 Observatory's activities. The following attachments were designed 

 for the 100-inch telescope: extra-focal interferometer, Cassegrain 

 spectrograph VI, Cassegrain spectrograph VII (for red end of spec- 

 trum), motor drive for mirrors of 20-foot interferometer, diaphragm 

 for end of tube, focusing apparatus for Newtonian plate holder, minor 

 improvements of dome and mounting, silvering appliances, instru- 

 ment cabinets, etc. Work for the 60-inch telescope included designs 

 for intensifier lens, modification of quartz spectrograph, finder mount- 

 ing, wind-screen motor mounting, and changes in counterweights. 

 Alterations of the Snow telescope involved improvements in the con- 

 cave-mirror mounting and speed reduction of the windlass. A new 

 focal-plane shutter and a plate-holder for the 13-foot spectrohelio- 

 graph were designed for the 60-foot tower telescope. Work for the 

 laboratory included improvements of the large solenoid magnet and 

 attachment, a vacuum furnace and hood, photographic recording 

 apparatus, and quartz tubes for the Stark effect. Other designs 

 were for a stereo-comparator micrometer, mirror mountings for the 

 velocity of light apparatus, and various mmor appliances. One drafts- 



