SECRETARY'S REPORT 119 



consequence the Smithsonian standard scale of radiation has been 

 made available throughout the whole world. 



Dr. Abbot, research associate since his retirement from administra- 

 tive work, continues his special studies, and Dr. Henryk Arctowski 

 continues his researches concerning solar and terrestrial atmospheres. 



Work in the field. — Last year's report mentioned the new concrete 

 observing tunnel on Table Mountain, Calif., about 100 feet west of 

 the old tunnel, in which the spectrobolometric equipment formerly 

 used at Tyrone, N. Mcx., had been set up. This gave duplicate equip- 

 ment in the two tunnels, and at the beginning of the year a series of 

 simultaneous observations was in progress, observing through iden- 

 tical skies. The series continued for 40 observing days, including 8 

 long-method days. Detailed comparisons of the observations showed 

 satisfactory agreement. One unexpected difference persisted through 

 the observations, namely, the ratio of the galvanometer deflections 

 for successive wavelengths changed progressively through the spec- 

 trum. The ratio ^llTnlTlftZ started at about 1.150 in the violet 

 end and decreased to 0.960 in the red end. These differences in de- 

 flections are compensated for by the transmission factors, which are 

 regularly determined for each individual spectrobolometer and the 

 deflections altered accordingly. 



Following this series of observations, the stellite mirrors in the new 

 tunnel were replaced by aluminized mirrors. As expected, this mate- 

 rially increased the deflections in the new tunnel — a gain of twofold 

 in the red end and approximately fivefold in the violet end. A second 

 series of simultaneous observations, one tunnel with stellite mirrors 

 and the other with aluminized, is now in progress. 



Mr. Hoover took with him to Table Mountain a specially built 

 double spectroscope with rock-salt prisms, designed to measure the 

 ozone absorption in the infrared, between 9 and 10 microns wavelength. 

 This was mounted and tested in the new tunnel. 



A new and important project has developed at Table Mountain, re- 

 sulting from a paper published in 1931 by Dr. Oliver R Wulf , of the 

 United States Weather Bureau and the California Institute of 

 Teclmology, on the determination of ozone by spectrobolometric meas- 

 urements (Smithsonian Misc. Coll., vol. 85, No. 9). Dr. Wulf has 

 long felt that a method could be developed for daily measurement of 

 the quantity of ozone in the upper atmosphere from the Smithsonian 

 solar-constant records. He bases his method on the relatively weak 

 Chappuis absorption bands in the yellow-orange region of the visible 

 spectrum. Dr. Wulf fortunately was able to spend some days on 

 Table Mountain, working on the details of his method. On February 

 1, 1951, the Table Mountain staff started the required daily measure- 

 ments. Preliminary results look promising, and the method will be 



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