in the Theory of Sound. 103 



opposite direction. For, on tlie 25th June, p. 452, the interval 

 is longer, even when sound could not be heard in the opposite 

 direction, than the mean of both directions on the 27th and 28tli 

 June *. This difference, I apprehend, has arisen from the dif- 

 ference of the guns/orof the mode of charging and firing them. 



When the production of sound is accompanied with intense 

 heat, as in the firing of guns, there is reason to think that a 

 portion of such heat is propagated from one portion of air to 

 another along with the sound. On this account, I conceive 

 that tlie report of a gun moves faster than the sound of a bell, 

 over and above what is due to superior intensity. As, however, 

 a bell is not Iieard at such a distance as a gun, and the methods 

 hitherto employed are too complicated for measuring with ac- 

 curacy or facihty the minute interval of time in which a sound 

 passes over a small distance, the exact velocity of sound from 

 bells has not yet been determined. I therefore beg to propose 

 the following simple expedient, by which I presume the diffi- 

 culty of measuring the minute interval of time would be entirely 

 obviated. I shall begin with a very familiar illustration of the 

 principle. 



Suppose a hammer, moved by clock-work, to strike a bell at 

 equal short intervals, as seconds, and that an obsei*ver sees the 

 hammer just touch the bell, at the very instant when he first 

 hears the sound. It is evident, that he must be either quite 

 near the bell, or at such a distance as requires exactly one se- 

 cond, or a whole number of seconds, for the sound to reach him •^. 

 By removing himself a very little farther off, the sound will ar- 

 rive too late, and by approaching rather nearer, the report 

 will precede the visible stroke. In short, a very small varia- 

 tion on the distance will sensibly disturb the coincidence ; and 



• In pages 430, 4.31, some experiments are mentioned as made in January 

 1823, which, from the rest of the article, seems so exceedingly improbable, 

 that I think the author or translator, not being alike familiar wdth both lan- 

 guages, has put January several times for June. 



f 1 here mention seconds for convenience ; but in practice, I suspect the 

 intervals must be at least of sufiicient length to keep the sounds of the 

 strokes quite distinct ; which, at any rate, will require very small intervals. 

 If the vibrations caused by music were quite clear of each other, the veloci- 

 ties of the notes might not be so nearly equal. 



