CHAP. I.] 



SOUND SIGNALS. 



113 



Mars to liueil ; they were very satisfactory. M. Sudre had reduced 

 the sounds to three notes : G, C, G. Later on he succeeded in not 

 using more than one sound, so that one note of the clarion, one "beat 

 of the drum or one cannon-shot, might at pleasure and according to 

 the circumstances be used as elements of military sound signalling. 

 A system of correspondence of this kind was established at Sebastopol 

 during the siege, and rendered service to the besieging army by pre- 

 venting the reserve from nocturnal attacks which the Russians 

 directed towards those working in the trenches. 



Musical signalling cannot rival either the electric telegraphy or 

 visible signals. But there are cases where neither one nor the other 

 of these can be employed, and where it can then be advantageously 

 adopted. 



IV. EAR-TRUMPETS THE STETHOSCOPE. 



The ear- trumpet is an instrument which has another kind of 

 interest, particularly appreciated by persons suffering from partial 

 deafness. It strengthens sounds, like the speaking-trumpet, by con- 

 densing them within a short distance and in the ear of the listener. 



FIG. (59. Ear-trumpets. 



The ear-trumpet is a conical tube, made in various forms, 

 which the deaf person holds m^the hand, introducing the Smaller 

 extremity into the ear, and turning the bell towards the mouth of 



I 



