120 ANNUAL ItEPORT SMITHSONIAN INSTITUTION, 1930 



wave-length regions, or colors, to determine where in the spectrum 

 the phototropic influence begins as one proceeds to shorter wave 

 lengths that is, from red to blue. For this purpose suitable screens 

 are not available and one must, therefore, turn to a monochrometer. 

 Such a monochrometer would be used, on the one side, to furnish 

 all the different possible wave lengths or colors, while on the other, a 

 single standard comparison source would be used. The phototropic 

 influence of all the various wave lengths, would be expressed in terms 

 of a single standard. As has been seen in the preliminary experi- 

 ment, some thirty thousand times variation in phototropic effect is 

 to be observed. The comparison light, must, therefore, be varied in 

 intensity over a large range. For this purpose an optical bench has 

 been purchased. By means of this bench, the comparison light may 

 be varied b}^ var^dng the distance from the plant over a range of 

 three meters. Since the intensity of light varies inversely as the 

 square of the distance from the source, this permits a tremendous 

 range of possible intensities. As funds v.'cre not available for the 

 purchase of a monochrometer, plans were made for the construction 

 of an instrument from optical parts available in tlie Smithsonian. 

 Lenses belonging to the National Museum, and originally used as 

 projectors, were loaned to the division for the construction of this 

 monochrometer. A prism and mirror were loaned by the Astro- 

 physical Observatory. A spectrometer bearing of a novel type, in- 

 volving an inverted cone with a ball thrust, was constructed by Mr, 

 Kramer in the Astrophj'sical Observatorj'^ shop. Because of the 

 I)ressure of other work in the shop, this monochrometer, begun in 

 February, was not completed until August of 1930. Preparations 

 for this more extensive experiment are now nearing completion. 



COOPERATION 



During the second half of the year. Doctor "Weniger from Oregon 

 State College came to the laboratory and undertook the development 

 of more sensitive radiometers for the xlstrophysical Observatory. 

 The facilities of the laboratorj^, and a considerable part of Mr. 

 Clark's time were placed at his disposal. At the termination of the 

 6-month period, it was necessary for Doctor Weniger to return to his 

 position in charge of the Physics Department at Oregon State Col- 

 lege. The completion of the development of these new radiometers 

 is, however, still in progress in his laboratory at Corvallis, Oreg. 

 The radiometers, when finally developed, will not only be of unusual 

 value of the Astrophysical Observatory in its study of stellar radi- 

 ation, but also to the Division of Radiation and Organisms in its 

 contemplated work in the infra-red spectrum upon the molecular 

 structure of polyatomic molecules. 



