SECRETARY'S REPORT 85 



rotates, the atmosphere of the bright hemisphere, directly subject to 

 solar radiation, exhibits a pronomiced bulge, wliile that of the night 

 hemisphere cools and contracts. In addition, the density of the 

 entire atmosphere above 200 kilometers fluctuates in response to 

 variations in the 20-cm solar flux, and undergoes transient, relatively 

 rare variations caused by great storms on the sun. Dr. Jacchia has 

 constructed a model atmosphere that accounts for these periodic 

 fluctuations, and has developed a formula that yields the proiile of 

 atmospheric density above any point of the earth at any time, given 

 the position of the sun and the value of the 20-cm solar flux. 



Tliis work has obvious practical application to geophysics and to 

 space science, and the U.S. Air Force is now partially supporting an 

 expanded program of research. 



Dr. Hynek and George J. Nielson continued their balloon experi- 

 ments in cooperation with the U.S. Air Force, Oflice of Scientific 

 Research in Washington, D.C., Air Force Cambridge Research Cen- 

 ter, and the Massachusetts Institute of Technology Instrmnentation 

 Laboratories. They now have scheduled unmanned balloon flights 

 in the late summer, 1960, and plan manned balloon flights at 90,000 

 feet altitude in the fall of 1960. These flights are designed to deter- 

 mine the amount of image distortion produced by the atmosphere 

 at altitudes between 50,000 and 100,000 feet and to study the use of 

 infrared tecliniques in stellar photography, and the feasibility of in- 

 strumenting and mannmg astronomical observatories in high-altitude 

 vehicles. 



Dr. Hynek and George G. Barton are investigating the possible 

 application of electronic image-converter tecluiiques to astronomy. 

 The preliminaiy system tests have been completed, and a program 

 begmi with the 20-inch Cassegrain telescope at Mount Palomar Ob- 

 servatory will permit comparison of observations made with image 

 orthicon techniques with those made by current photographic 

 techniques. 



Dr. A. V. Baez devised a method of obtaining high resolution 

 photographs with short wavelengths diffracted and focused by spe- 

 cially constructed Fresnel zone plates. He has also developed a re- 

 flecting X-ray "telescope" constructed of an array of crossed plane 

 mirrors which simulate a matrix of collimated pinholes brought to 

 a conmion focus. He is now working on an advanced version of this 

 device which will use curved instead of plane mirrors. These devices 

 will eventually produce an X-ray telescope for observations in the 

 extreme ultraviolet and soft X-ray regions above the earth's 

 atmosphere. 



The Director and Dr. Davis continued the development of a tele- 

 scope for use in space, the "Celescope." Specifications for the vari- 

 ous components were completed, and the contract was awarded to 



