88 EXPERIMENTS IN AERODYNAMICS. 



most mobile gas may be practically as great as we please and, with explosive 

 velocities, for instance, may be as great as would be the reaction of a mass of iron. 

 The theory of aerial propellers being that for a maximum efficiency, the 

 higher the velocity, the sharper should be the pitch of the blades, it has been the 

 object of the complete series of experiments with the Bi/namometer-Chronograph 

 to determine by actual trial the velocity of advance at which the maximum 

 efficiency is attained when the blades are set at different angles, and the best 

 forms and dimensions of the blades. The details of these are reserved for future 

 l>ublication, but, very generally speaking, it may be said that notwithstanding 

 the great diiference between the character of the media, one being a light and 

 very compressible, the other a dense and very incompressible fluid, these observa- 

 tions have indicated that there is a very considerable analogy between the best 

 form of aerial and of marine propeller. 



