38 REPORT — 1870. 



there exists no valid ground for a distinction between light and heat in this respect 

 is further confirmed by the experiments of ]\Ir. B. Stewart, who has shown that 

 the emission of light by incandescent bodies closely corresponds with their absorp- 

 tive power (whether selective or otherwise) when not incandescent, and, further, 

 that even in the decomposition of light into two polarized beams by the tourmaline, 

 that substance emits when incandescent the ray that is otherwise absorbed. Can 

 there, then, be any valid reason for doubting the ability of ordinary matter to trans- 

 mit those transverse vibrations which it is obviously capable of either absorbing or 

 emitting ? and if so, what ground is there for the hji-pothesis that the transmission 

 of light- and heat-waves necessitates the presence of imperceptible tether in the 

 interstices of perceptible matter ? 



If the existence of sether in infinite space, essential to the undulatory theory, be 

 admitted, it may be asked how is it possible to conceive its exclusion from any por- 

 tion of space ? A very simple hypothesis, propounded by the writer in the Intro- 

 duction to the last edition of his ' Elements of Physics,' will meet tliis difliculty — 

 namely, that asther (like its fluid namesake with water) is immiscible with known 

 gaseous matter. This, it must be admitted, is sheer hypothesis ; but if true, it must 

 ever remain so, sether being in that case beyond the reach of human ken : of this 

 we may, however, rest assured, that if it be not wanted in and around even our 

 corporeal frames, it is not there ; the contrary supposition would be inconsistent 

 with the infinite wisdom of the Creator of the universe. 



On certain Objections to the Bynamie Theory of Heat. 

 By H. Whiteside Cook. 



In this paper the author first endeavoured to show that heat must necessarily be 

 a force of a permanent nature, could not possibly be a mere affection of matter, and, 

 as is asserted by the believers in the " Djaiamic " hypothesis, that it must bo in 

 the nature of an " energj'," and not an " impulse." 



He then proceeded to analyze the nature of heat as described in the thermo- 

 dynamic theory, and brought forward arguments to show that the causes Avhich 

 produce heat would not produce the molecular motion presumed, and that, on the 

 other hand, allowing this molecular motion to exist, it would not produce the effects 

 which are produced by heat. He proceeded, in conclusion, to consider one or two 

 of the experiments on which the djTiamic h\'pothesis was based, and showed that 

 they were in no way incompatible with the old theory of a caloric or substantive 

 heat. In short, the argument of the paper was : — tliat though such forces as 

 electricity, magnetism, &c. were probably justly considered to be only affections 

 of matter, it was a mistake to conclude the same thing of heat ; that if the attracti- 

 vity of matter be apenuanent energetic force, then heat,tlie force which counteracts 

 that attractivity among molecules, must also be a permanent energetic force ; for a 

 force of impulse cannot cope -with a perpetual energetic force ; however great the 

 irapidse, it must soon be beaten ; and were heat a condition and not an entity, 

 then it would be but a passing phenomenon. 



In dealing with the experiments which are supposed to substantiate the dynamic 

 hypothesis, the author dwelt especially on Davy's celebrated experiment of liquefying 

 ice by friction, when he showed that the increment of heat added to the ice was 

 very small in comparison with the amoimt of heat contained by the ice when at the 

 temperature of 82 Fahr., and that the molecular agitation to which it was subjected 

 would cause it to absorb this heat from the atmosphere of caloric, which, on the 

 substantive theory, would ex hypothesi surround it. He next spoke of the fall of 

 temperature which takes place when compressed air is allowed to escape from 

 the confining vessel (an experiment which is put forward by the exponents of the 

 dynamic theory as instancing the conversion of heat into mechanical energy), and 

 pointed out that in the preparation of the experiment the compression of "the air 

 had forced out of it some of the heat that it contained. When, then, it was allowed 

 to escape, the air brought out less heat than it took in, the difference being the 

 amount which had been given out in cooling after the original compression. The 

 author added that these experiments could not be said to substantiate the dynamic 

 theory — and that if he did not mention more of them, it was because those present 



