POLYTECHXIC ASSOCIATION. 781 



when tlie steam condenses, and there is another precipice, and 962 

 units of heat are set free. Coming down another incline for 180°, a 

 third precipice, on the formation of ice, sets free 142 units of heat ; 

 and from that point the descent is continuous to the point of absolute 

 cold. Tyndall compares the falling of the atoms of oxygen upon car- 

 bon to the falling of meteorities into the sun in explaining the pro- 

 duction of heat. 



The President — The theory of the oscillation of atoms was long 

 ago advocated by Rankin. The revolution of atoms in a system was 

 first presented before this Society in a new theory by Professor Wal- 

 ling. 



Dr. Yan der Weyde — I do not claim as my hypothesis that heat 

 is atomic motion ; but I have never seen any consistent explanation 

 how the oscillating motion of atoms in solids is connected with the 

 motion in straight lines in gases. 



Dr. J. W. Richards — This hypothesis gives a better explanation 

 of the paradox that water begins to expand at forty degrees than I 

 have before met with. 



Dr. Yan der Weyde — One point about the velocity I forgot to 

 state. As the temperature rises, and the velocity increases, chemical 

 decomposition takes place. In the spectrum, where the velocity of 

 the nndulations is the greatest, chemical action takes place. 



The President — It is amplitude of the seth-wave, and not its 

 velocity, that produces intensity of heat. 



Dr. Yan der Weyde — So long as the velocity of the wave is below 

 400,000,000,000 in a second we do not see anything. At that point we 

 see red light. When it reaches 900,000,000,000 it has passed through 

 the spectrum, passed the violet, and again reached a point where we 

 do not see anything. At any temperature, there may be waves of 

 lower velocity mixed with those of higher velocity. There may be 

 invisible waves mixed with visible waves. With the higher veloci- 

 ties the waves are so short, perhaps they get between the atoms, and 

 therefore chemical decomposition takes place. 



Mr. D. Blanchard — One point seems to me inconsistent. The 

 difference between great oscillation, through nearly the whole circle, 

 and rotation, is infinitely small, and yet a great amount of heat is 

 employed to produce that difference. 



The President — Intensity of heat is produced entirely by the 

 amplitude of the wave, and not at all by its length. The pitch of a 

 sound depends upon the number of waves in a given time ; but the 

 loudness of a sound does not depend at all upon that, but wholly 



