MOUNT WILSON SOLAR OBSERVATORY. 



243 



The conditions of seeing on a scale of 1 to 5 and the wind records are 

 given in the following table : 



During the year the U. S. Weather Bureau installed at the Observa- 

 tory a Marvin automatic recording rain-gage, maximum and minimum 

 thermometers, and a Richard thermograph. In addition to sending 

 written monthly records of meteorological data, Mr. Hoge, night assist- 

 ant with the 60-inch reflector, furnishes each morning to the Los Angeles 

 office of the Weather Bureau, telephonic reports of the current weather 

 conditions which are being included in the daily weather charts pub- 

 lished by the Bureau. 



The total precipitation at Mount Wilson during the year ending 

 August 31, 1916, was 36.75 inches, of which the snowfall amounted to 

 49 inches. The liighest temperature was 93° F. on July 11, while the 

 lowest was 14° F. on January 30. 



MONOCHROMATIC PHOTOGRAPHY OF JUPITER AND SATURN. 



The important results obtained by Professor Wood through mono- 

 chromatic photography of the moon with ray-filters transmitting hmited 

 regions of the spectrum made an extension of this investigation to the 

 planets of exceptional interest. Accordingly the 60-inch reflector was 

 placed at his disposal for four nights in October of last year, and a 

 complete series of photographs of Jupiter, Saturn, and the Moon was 

 secured by him at that time. 



The photographs were made at the 80-foot focus of the reflector, 

 the regular double-slide plate-carrier being employed for the purpose. 

 Four ray-filters were used. The filter for ultra-violet light consisted 

 of a bromine cell 5 mm. in thickness, with uviol glass windows, which 

 was placed directly in front of the photographic plate. In case a very 

 restricted region of the spectrum was desired this filter could be 

 supplemented by a cell containing a very dilute solution of potassium 

 chromate. The two filters in combination transmit the spectral 

 region from X2900 to X3250. The remaining filters consisted of 

 stained gelatine films mounted between thin sheets of plate glass, and 

 transmitted respectively X 4000 — X 4500, the region above X5000, and 

 the region above X 7000. 



