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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



different distances from the nose. This gives the Mach number of the 

 flow past the rocket, and hence the speed of sound. 



Indirect evidence about the temperature distribution has been ob- 

 tained from a study of atmospheric tides. It has been found from 

 radio observations (see below) that the amplitude of the lunar tidal 

 oscillations is greatly enhanced at the level of the E layer. The am- 

 plitude and phase of these oscillations at high levels are quite sensitive 

 to the temperature distribution, and Weekes and Wilkes [1] ^ were able 

 to show theoretically that up to 100 km. the general form must be that 

 shown in figure 2. 



High-temperature layer 



Gunfire 



Ionized layer 



V/////////////A 



Figure 3. — Illustrating the long-range propagation of radio and sound waves. 



Finally, it has been possible to obtain information about the tem- 

 perature in the E and F layers by determination, by means of radio, 

 of the variation of electron density with height. The scale height H^ 

 which is the distance above a given level at which the pressure has 

 fallen to \/e of its value at that level, is given by n=RT/Mg, where 

 R, r, and M are as previously defined and g is the acceleration due to 

 gravity. Assuming the atmospheric composition, the temperature T 

 may be deduced if H is known. Allowance must be made for dissocia- 



' Numbers in brackets Indicate references at end of text. 



