REPORT OF THE SECRETARY 119 



tinuous observations at Camp Lee. These records give the sun and 

 sky radiation in calories per square centimeter, for each hour of each 

 day divided as follows : 



(1) Total intensity on a horizontal surface. 



(2) Total intensity on a surface inclined 45° to the east. 



(3) Ultraviolet intensity on a surface 45° to the east. 



(4) Visible intensity 45° to the east. 



(5) Infrared intensity 45° to the east. 



(6) Intensity under a vycor filter which transmits all radiation, inclined 45° 



to the south. 



(7) Intensity under a black filter (Corning 2540) which cuts off the ultra- 



violet and visible, and transmits the infrared, 45° to the south. 



(8) Intensity under a yellow filter (Corning 3385) which cuts off the ultra- 



violet and transmits the visible and infrared, 45° to the south. 



(9) Ultraviolet intensity on a horizontal surface measured with a special 



photoelectric ultraviolet meter. 



The measurement and reduction of these voluminous records have 

 been tedious and time-consuming. Integrating devices which will 

 greatly simplify the work are being studied by Mr. Hoover and L. B. 

 Clark, and several such devices are under construction in our shops. 



It is now 13 years since Dr. C. G. Abbot and the Director last deter- 

 mined the standard scale of solar radiation on Mount Wilson. In 

 anticipation of a new determination of this scale in the near future, 

 the double-barreled water-flow pyrheliometer used successfully in 

 1934 has been partially rebuilt. Rubber joints within the instrument 

 have been eliminated, copper-constantan thermojunctions replace the 

 former nickel-platinum junctions, and the thermoelement arrangement 

 is made more simple and efficient. 



Dr. Abbot, research associate of the Observatory, has continued his 

 studies of the effects of solar changes on weather. He has also experi- 

 mented with a small solar engine, and has made preparations for a 

 further study of the energy spectra of stars which he will undertake 

 soon with the aid of the Mount Wilson 100-inch telescope. 



At the request of Dr. Henryk Arctowski, and with the cooperation 

 of Dr. Abbot and the Secretary of the Institution, Dr. Alexander 

 Wetmore, arrangements were made for John McLean Hildt to come 

 to Washington to assist Dr. Arctowski for 1 year. Mr. Hildt, form- 

 erly meteorologist for the American Overseas Airlines, began work 

 with Dr. Arctowski on June 2, 1947. He will help organize and pre- 

 pare for publication the large amount of material which Dr. Arctowski 

 has accumulated. 



Worh in the -field. — In October 1946 Mr. Hoover and Paul Greeley 

 went to New Mexico and packed for shipment the entire equipment 

 of our Tyrone station, closed since February 1946. Arrangements 

 were made for the sale and disposal of the buildings and for the return 



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