114 Soimd Waves in the Atmosphere. 



Moreover, from (47) the equation of the envelope reduces to 



W ,(£)*"*=2A-B, ..... (49) 



where B= j (l^" 



Comparison of (46) and (49) shows that the envelope and 

 curve of vertices are similar curves, of the type 



d?2*<»-.2) = const. 



Fig. 7 shows a sketch of the loci. 



Fig. 7. 



Carve of vertices 



Those of the results here given which were obtained whilst 

 the author was a member of the Munitions Inventions Depart- 

 ment are published with the consent of that Department. 



Trinity College, Cambridge, 

 14th February, 1921. 



