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ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 7 



the sky. Within recent years the photographic method has been 

 developed to a high level of sensitivity with its natural accompani- 

 ment of extreme precision in the measurement of heights, trajectories, 

 and velocities. Even more recently an entirely new technique, the 

 measurement of radio reflections by radar methods, has become a vital 

 tool in the study of meteors. 



BRt^ 





Figure 3. — Diagram showing a meteor photographed simultaneously from stations A and 

 B; the circle represents a common point on both photographs of the trail. 



Let us begin with the photographic techniques and follow them 

 with a resume of the radio techniques for studying meteors. The 

 first long and systematic photographic meteor program was con- 

 ducted by Elkin of Yale Observatory from 1893 to 1909 (see Olivier, 

 1937). He used two telescopes (fig. 3) and in front of each telescope 

 he placed a rotating shutter and recorded its speed of rotation by 

 means of a chronograph. Unfortunately, he used such a short base 

 line, about 2 miles, that the geometry of most meteor trails was 

 poorly determined, so that he could not obtain accurate heights, 

 velocities, and trajectories of meteors. In 1936 the writer initiated 

 a similar method (Whipple, 1938, 1940), making use of the two sta- 

 tions operated by the Harvard College Observatory in Cambridge, 

 Mass., and at Harvard, Mass., about 24 miles apart. The small Har- 

 vard patrol cameras at these two stations simultaneously photo- 

 graphed approximately half a dozen bright meteors per year. 



After World War II, meteors and related upper-atmospheric 

 problems and supervelocity ballistics became of such interest that the 

 United States Naval Bureau of Ordnance supported an extensive 



