48 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



which quickly opened and closed the shutter precisely on the desired 

 seconds. The thermoelement leads were fed through an amplifier to 

 a Leeds and Northrup micromax recorder. Several sets of compari- 

 sons were made between the automatic recorder and a silver-disk in- 

 strument read as usual. These preliminary readings looked very 

 promising and it is hoped in the near future to make further compari- 

 sons to determine the relative accuracy of this, the first automatically 

 recording silver-disk pyrheliometer. 



Work in the field. — At Montezuma, Chile, a change in personnel 

 occurred in June 1954. John A. Pora, for five years assistant observer 

 at this station, returned to Washington. Dr. James E. Zimmerman 

 of our Table Mountain (Calif.) staff replaced him at Montezuma. 

 Mr. Pora after an extended leave will proceed to Table Mountain. 



The Coast and Geodetic Survey has assigned a new seconds-pendu- 

 lum precision clock to the Montezuma station, for use in the seismo- 

 graphic work referred to in last year's report. 



At Table Mountain several special projects mentioned in previous 

 reports have continued in operation. Further tests with the Harvard 

 photometer and the filter pyranometer were made. The ozone studies, 

 sponsored by Dr. Oliver R. Wulf, were materially aided by Dr. Zim- 

 merman of our staff. This work is described in a paper by Drs. 

 Wulf and Zimmerman entitled "A Method for the Measurement of 

 Atmospheric Ozone Using the Absorption of Ozone in the Visible 

 Spectrum," soon to be issued as vol. 123, No. 3, of the Smithsonian 

 Miscellaneous Collections (Publication 4177). 



In 1952 Mr. Hoover and Mr. Froiland mounted the standard water- 

 flow pyrheliometer at Table Mountain and made a long series of com- 

 parisons against silver-disk pyrheliometer S. I. 5. The standard in- 

 strument was then dismantled and returned to Washington. To set- 

 tle an uncertainty which has arisen in discussing pyrheliometers with 

 Dr. Abbot, it seemed advisable to return the standard to Table Moun- 

 tain and have Mr. Froiland remount it as it was in 1952. The un- 

 certainty concerned the magnitude of the error due to outgoing radia- 

 tion to space emitted through the aperture of the pyrheliometer and 

 also due to brightness of the sky around the sun visible through the 

 aperture. Before shipping the instrument, Mr. Harrison built a 

 plastic airtight box around the thermo junctions of the water-flow 

 pyrheliometer to reduce drift due to convection currents. As the re- 

 sult of Mr. Froiland's tests it is concluded that in clear skies the re- 

 sulting error is negligible. 



DIVISION OF RADIATION AND ORGANISMS 

 (Report prepared by R. B. Witiirow, chief of the division) 



The form assumed by higher green plants under favorable condi- 

 tions is determined by heredity and the complex of environmental f ac- 



