424 Mr. J. R. Harrison's Experimental Researches 

 The ratios of energy are : — 



transmitted _ b 2 

 incident — A 2 + B 2 



_ JL T -2ABcos7±4(VA 2 + B 2 -ABcos7 \ 

 ~ 9 t A 2 + B 2 J' 



single reflected stream _ a 2 



incident "" A 2 + B 2 



_,/<>, ABcos 7 +2G^A 2 + B 2 -ABcos7\ 



-~n z+ ~ a 2 +b 2 ~y 



If y = 0, or cos 7 = 1, and A = B, we have the case of prop. V. 

 This determines the employment of the upper signs before the 

 roots in the present results, in which case these results coin- 

 cide with those of prop. V., giving § of the whole transmitted, 

 and the remaining -J- divided between the reflected streams. 

 If cos 7 = 0, or the component systems differ in phase by \ of 

 a period, the whole energy is transmitted, or the geometrical 

 composition takes place unaltered. This is immediately seen 

 from the vanishing of the term (2AB cos 7), by which C 2 dif- 

 fers from A 2 + B 2 . 



In all these discussions it has been assumed that the incident 

 wave-systems were not subject to constraint, which would pre- 

 vent them from yielding to the reflected impulse ; and in cases 

 of interference in air constraint is frequently absent. But 

 where the two wave-systems are supplied, say, by tuning- 

 forks close to the point of meeting, the forks are capable of 

 maintaining their movement unchanged and acting as a con- 

 straint. Under these circumstances more work is done by the 

 sources, and the geometrical composition of the systems is 

 maintained. 



In the next note I propose to apply the principle of the flow 

 of energy to the divergence of sound in air. 



LYII. Experimental Researches on the supposed Diathermancy 

 of Rock-Salt. By John Rushton Harrison*. 



[Plate III.] 



IT is almost universally accepted that pure rock-salt trans- 

 mits more than 92 per cent, of the total radiation from 

 heated bodies. I would ask permission to glance for a moment 

 at the mode of experiment by which Melloni arrived at this 

 conclusion. 



* Communicated by the Author. 



