136 • Mr Ritchie on Radiant Heat. 



more correct than that which I have hitherto adopted. I have 

 the honour to be, Sir, your most obedient servant, 



WiESENAU, October 23, 1826. F. T. Bueg. 



Art. XXIII. — Excursory Remarks an Radiant Heat, Tenth 

 a short examination of' Professor Leslie'^s Theory/. By 

 William Ritchie, A. M. Rector of the Royal Academy 

 at Tain. Communicated by the Author. 



Professor Leslie, in his ingenious works on heat, endea- 

 vours to account for the various phenomena of radiant heat, by 

 supposing that caloric is carried from a heated body to another 

 at a distance, by certain pulses excited in the ambient air. 

 " By wh^t process the several portions of heat thus delivered 

 to the atmosphere shoot throfigh the fluid mass, it seems more 

 difficult to conceive. They are not transported by the stream- 

 ing of the heated air, for they suffer no derangement from the 

 most violent agitations in that medium. The air must there- 

 fore, without changing its place, disseminate the impressions 

 that it receives by a sort of undulatory commotion, like those 

 by which it transmits the impulse of sound. The portion of 

 air next the hot surface suddenly acquiring heat from its vi- 

 cinity, expands proportionally and begins the chain of pulsa- 

 tions. In again contracting, this aerial shell surrenders its sur- 

 plus of heat to the one immediately before it, and which is now 

 in the act of expansion ; and thus the tide rolls onwards and 

 spreads itself on all sides.'*''* If air be the medium of commu- 

 nication, we may ask how it happens that caloric radiates more 

 rapidly in the most complete Torricellian vacuum than in at- 

 mospheric air of any density whatever ; or why it radiates more 

 copiously in rarified than in condensed air ? Sir Humphry 

 Davy has proved, by a very simple and ingenious experiment, 

 that in air exhausted to the 120th part of the whole, the effect 

 of radiation was three times greater than in air of the common 

 density. An explanation of his method may be seen in Dr 

 Henry's Elements of Chemistry, vol. i. 83. The same fact 



• lUlations of Air to Heat and Moisture, page 21. 



