OHAP. 1.] 



SOUND-SIGNALS. 



Ill 



we are indebted for it to Samuel Moreland, 1670. A glass or copper 

 trumpet was first used. 



Since that time, elliptical, hyperbolic, and various other forms have 

 been given to these instruments, and a theory has been formulated to 

 explain the strengthening of the sound by the successive reflections of 

 the sound-waves on the inner walls of the tube. According to Lam- 

 bert, the wide conical form has the effect of rendering the reflected 



FKJ. OS. Speaking trumpet in tin- ineivliunt service. 



rays on leaving the tube parallel to the axis in such a manner that they 

 are all directed towards the point to which the sound is required to be 

 carried. The surfaces which are convex towards the axis are therefore 

 useless. But Hassenfratz found by experiment, with two similar 



