1874] WRITINGS OF JOSEPH HENRY. 



The following table gives the results: 



401 



From these experiments it would appear that the material 

 or elasticity of the trumpet had little or no effect on the 

 penetrating power of the sound, although the shape appeared 

 to have some effect, the pyramidal trumpet, or one with 

 square cross-section (No. 1) giving a less result than the con- 

 ical ones of the same sectional area. A comparison was 

 made between a long straight trumpet and one of the same 

 length curved at its upper end, which gave the same pene- 

 trating power with the same pressure. It is probable that 

 a thin metallic trumpet would give greater lateral diver- 

 gency to the sound, and also a slightly different tone. 



8. The effect of a hopper-formed reflector was next tried 

 with the whistle, the axis of which was about 5 feet in length, 

 the mouth 6 feet square, and the small end about 18 inches. 

 When the whistle was sounded at the small end of this 

 reflector, the distance at which the sand ceased to move was 

 51 ; the sound of the same whistle without the reflector ceased 

 to move the sand at 40. The ratio of these distances would 

 have been less with a more sensitive instrument at a greater 

 distance on account of the divergency of the rays. 



9. In order to determine the diminution of sound by de- 

 parting from the axis of the trumpet, a series of experiments 

 was made with a rotating trumpet, the axis of which was at 

 first directed along the graduated line of observation, and 

 subsequently deflected from that line a given number of 

 degrees. The following were the results: 



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