SOLAR RADIATION ABBOT 



119 



which automatically measures the spectrum energ}^ Absorption 

 effects are produced on the infra-red rays. These effects are found 

 to be characteristic for each chemical studied. In this way we are 

 building up a system of organic chemical analysis, whereby chemical 

 structure can be determined without making combustions. It is yet 

 uncertain how powerful this method will eventually prove, but we 

 hope it will throw much light on the abstruse reactions of plant 

 growth under the influence of radiation. 



PflRflDICHLORBENZENE 



P/^RftDIBROM BENZENE 



PflRnni lODOBENZENE 



I ^ T 



FiGDRB 8. — Absorption spectra of benzene derivatives. Observed undL-r the direction 

 of Dr. F. S. Brackett, Smithsonian Institution 



Plate 2 shows an experimental cooking plant which I erected at 

 the Smithsonian station on Mount Wilson. Sun rays falling upon 

 the great concave cylindric mirror, 7 by 12 feet in surface, and moved 

 by clockwork to follow the sun, are reflected upon a blackened brass 

 tube incased by a vacuum-glass jacket. Within the tube, which lies 

 parallel to the earth's axis, is high-test engine cylinder oil. It 

 grows hot, expands, and rises up into a reservoir containing about 

 60 gallons of oil. Two ovens for cooking are inserted in this reser- 

 voir of hot oil. A return tube from its bottom completes the circula- 

 tory system, bringing cooler oil to be heated by the mirror. For 



