AGGREGATE EFFECT OF INTERFERENCE. 171 



then the two kinds of heat correspond, the one to vibrations, or transmission 

 due to vibrations ; the other to transmission due to excess of elasticity, our 

 analysis teaches us to expect that the quantity of the former kind stopped 

 by the wires or scratches should be in exact proportion to the space covered 

 by them, whilst we should hardly expect to find any considerable stoppage 

 effected on the latter. Thus I am led to hope that the Theory which I pro- 

 posed in the Transactions of the Cambridge Philosophical Society, Vol. vi., 

 pp. 274, and seq. and subsequently developed in my little work on the 

 subject, will be strengthened in some points, although I am far from 

 expecting that it will be confirmed in all. Perhaps subsequent results may 

 render it necessary to modify our hypotheses, but at present I do not know 

 that experiment is very far in advance of theory. I cannot conclude with- 

 out expressing my conviction that the masterly researches of Professor 

 Forbes will have the effect of setting right several errors even in the Theory 

 of Light, which have crept in from the difficulty of subjecting that branch 

 of philosophy to strict measurement. 



P. KELLAND. 



Edinburgh, 

 Jan. 23, 1840. 



Y2 



