REPORT OF THE SECRETARY 101 



In May 1938 Mr. Hoover went to Mount Wilson to prepare for 

 new measurements of the energy in the spectra of the stars, and to 

 make studies of the growth of plants in monochromatic rays, taken 

 from sunlight by Christiansen filters. It may be said, by anticipa- 

 tion, that in both researches Mr. Hoover has been able to make 

 gratifying progress, as will be reported next year. It may even be 

 said now with confidence that when the 200-inch telescope is avail- 

 able it will be possible to get excellent continuous stellar spectrum 

 energy curves for all types of stars. Thus far Mr. Hoover has suc- 

 ceeded in measuring electric currents with his 17-ohm galvanometer 

 of 1X10 -12 amperes, and to observe the rays of a candle flame on a 

 thermoelement of 1 millimeter diameter from a candle distance of 

 150 meters. 



ATMOSPHERIC TURBIDITY AND MOISTURE APPARATUS 



In 1930 we constructed a special instrument, containing a spectro- 

 bolometer, an Angstrom pyrheliometer, and a pyranometer, for the 

 use of Mr. Moore in testing the availability of mountain sites in and 

 near Africa for solar-constant work. With this portable instrument 

 he could determine the total precipitable water in the atmospheric 

 path of sun rays, as well as total intensity of solar radiation, and 

 the brightness of the sky. This instrument came to the attention of 

 the United States Weather Bureau, and was considered to be of much 

 promise for their work. At the request of Chief Gregg, the Smith- 

 sonian Institution has undertaken to duplicate it for the Weather 

 Bureau, and the instrument maker, Mr. Kramer, is at work thereon. 



UTILIZING SOLAR RADIATION 



Some further progress has been made by Dr. Abbot on devices for 

 utilizing solar radiation. While in Florida, in March, he tried out 

 with gratifying results a solar flash boiler, a solar water distiller, 

 and a toy solar cooker. 



FIELD STATIONS 



Several considerations led to the abandonment of the Mount St. 

 Katherine solar-radiation station in December 1937. The isolation of 

 the station made its occupation hazardous. Its remoteness and isola- 

 tion made its upkeep costly. An intestinal infection attacked all of 

 the observers and proved stubborn to cure. The likelihood of a great 

 European war made it probable that the observatory might be wholly 

 cut off from Washington. The station was abandoned with regret, 

 for meteorologically it had proved to be excellent, perhaps equal to 

 Montezuma. 



