PROPAGATION OF SOUND. 347 



continuous functions into the solutions of partial 

 differential equations, belong to the history of pure 

 mathematics. Those which really concern the phy- 

 sical theory of sound may be referred to the pro- 

 blem of the motion of air in tubes, to which we 

 shall soon have to proceed ; but we must first speak 

 of another form which the problem of vibrating 

 strings assumed. 



