.aniiiuiir On the Propagation o/ Somjw^SV a'isJioT .Wi*I 



coefSeient as a measure of the intensity, and putting N ; 1 |<M' 



the ratio in which the intensity is diminished whde the sound 



travels, without divergence, over a length x, we get a-jul ihuh lo. 



log,„N = 0-0001 156y.r, . :^nvy>([t, sMqi) 



■■■ . • :,.!Ii>.ir.i jlliin.v 'VnA') 



the trnits of time and space to wmch q anda;j,fj:e,,i?Espectfiyely 

 referred being a second and a foot. in 



From the account of INI- Biot's experiments given hy Sir Jojb^^i 

 Herschel in ai-t. 24 of his Treatise on Sound*, it would seem 

 that the diminution of intensity which we can by any possibility 

 refer to radiation must be very small, especially when we re- 

 member that, in the case of these experiments, the intensity 

 would be diminished by a sort of reflexion at the bendings of the 

 tube, as well as by the friction of the air against the sides of the 

 tube, and th6 internal friction of the air itself. That the cause 

 last mentioned would produce a small but not utterly insensible 

 effect in causing a diminution of intensity, I have sliown in the 

 course of a paper " On the effect of the Internal Friction of 

 Fluids on the jNIotion of Pendulums," recently read before the 

 Cambridge Philosophical Society. If we suppose, at a venture, 

 that a diminution of intensity in the ratio of 2 to 1 is the utmost 

 which we can attribute to radiation in the case of M. Biot's ex- 

 periments, putting N = 2, and ^=3120, the length of the tube 

 in feet, we get from (20.) q=:0SS4 for a superior hmitof q. If 

 we suppose 5 = 0-834, we get for the ratio in which the tempe- 

 rature of a small portion of slightly heated air would be dimi- 

 nished in the course of one second, 1 to e~', or 1 to 0-4343, or 

 7 to 3 nearly. It is curious that it should, theoretically speaking, 

 be possible to assign a superior limit to the velocity of cooUng 

 of heated air by observations on sound ; but I imagine that the 

 real value of 5 is a good deal smaller tlian any limit wliichiil^ 

 wo\ild be practically possible to assign in this way. 



As the present communication is not exactly intended to be 

 controversial, I refrain from criticising the strange process by 

 w Inch Professor Potter attempts to obtain a new value for the 

 velocity of sound. •. . ^-^v., , j. j...; 



Pembroke College, '«' ^'^S adt ni 3-ii;aa'jiq ar 

 ■- Feb. 6, 1851.— . '^0 V'— -f- ■ '' - --i^n-;, ,c 



^•'P.S. The above paper was written and fonvarded to the edftors 

 before the publication of an article by Mr. Rankine, which has 

 appeared in the INIarch Number, otherwise I should have con- 

 tented myself by simply referring to Mr. Rankine's paper, so far 

 as relates to the point there discussed. 



I have supposed, as was already obser\ed, that radiant heat is 



.t^knoOt. f, Enayclopadia Metropolltaiia. RTt. Sound. 



