MOUNT WILSON OBSERVATORY. 257 



For the study of emission and absorption spectra at very high tem- 

 peratures, a tube furnace has been constructed of the type regularly 

 used in the laboratory, but with water-cooled contact-blocks of large 

 size designed to carry especially heavy currents. The furnace-tube is 

 protected by a large water-jacket. This furnace has proved entirely 

 suitable for the purpose intended, long runs at temperatures above 

 3,000° C. being possible, while but a few minutes are required to put 

 a fresh tube in position. 



An optical pyrometer of the disappearing-filament type, made ac- 

 cording to the Morse patent by the Leeds and Northrop Company, has 

 been purchased and has proved useful in furnace work where focusing 

 on the incandescent object was desired. 



A krge condenser, of about one microfarad capacity, charged from a 

 26,000-volt transformer, with rectifj-ing de\dce, was constructed for 

 experiments on the spectra of explosions. 



A 2-inch concave gi-ating which the laboratory has owned for several 

 years has been mounted for use with parallel light in a small wooden 

 spectrograph. This instiaiment is designed for use as an auxiliarj^ 

 dispersion piece for work with the interferometer in the red and infra- 

 red. With it the interference spectrum of iron has been obtained in 

 good focus from X5500 to X8000 on a scale of about 19 a per millimeter. 

 For the extension of wave-length standards into the region of longer 

 wave-lengths this instnmient is pro\'ing very useful. 



A set of six interferometer plates of crystalUne quartz has been 

 made for the laboratory in the optical shop. The figuring is now so 

 nearly complete that the plates are ready for final testing under actual 

 working conditions. They will form a valuable addition to our 

 present equipment, especially now that the fused-quartz plates are in 

 use on the mountain. 



To produce the monochromatic light necessary in many optical tests 

 and to supply a very useful working standard of wave-length, a Cooper- 

 Hewitt mercurj^-vapor Lamp has been installed in the laboratory. Its 

 great intensity, uniformity, and convenience have made it practically 

 indispensable. 



ELECTRIC-FURNACE INVESTIGATIONS. 



The study of the verj^ rich spectra of the rare-earth metals has been 

 taken up by Mr. King with the electric furnace. In addition to those 

 previously made for cerium, spectrograms at various temperatm'es, and 

 in some cases with different compounds, have been made for zirconium, 

 lanthanum, neodymium, and yttrium. Though the examination of 

 these plates is incomplete, the distinctive features of furnace spectra 

 are found to be well represented, a group of low-temperature lines being 

 present, with other groups appearing as the temperature is raised. 

 Many strong lines require very high furnace temperatures before they 

 appear. 



