Polytechnic Association. 779 



that 8,000 units of heat are set free in the combustion of hydrogen^ 

 that sufficiently accounts for the heat of the combustion, and there is 

 nothing mysterious about it. 



I now come to my hypothesis. Heat being a mode of motion, the 

 question arises, what kind of motion it is. It must, of course, be a 

 motion of the molecules. We have substances in four forms : solids, 

 liquids, gaseous and disassociated gases. In the solids we find a 

 tendency to crystallization. There is a certain polarity of the particles 

 of which the crystal form is the expression. I propound the 

 hypothesis that in solid bodies the atoms are all the time oscillating, 

 and that when we raise the temperature of a solid body we simply 

 increase the amplitude of oscillation. We know that as we raise the 

 temperature bodies expand, and oscillation with a greater amplitude 

 of course requires more space. The velocity of the oscillation is very 

 likely 400,000,000,000 in a second, between that of the electric and 

 of the luminous waves. 



Mr. Blanchard — Suppose the atoms are round? 



Dr. Van der Weyde — They are not round. How can an atom, or 

 rather molecule, of water be round, when it is composed of two 

 atoms of hydrogen and one of oxygen ? Molecules of water are not 

 round ; they have poles. They are centers of forces, but they have 

 polarity ; otherwise crystallization could not take place. The incredu- 

 lous man may examine the forms of snow flakes, and see the polarity 

 of atoms of ice. 



Now let us raise the temperature of our oscillating atoms of ice, 

 increasing the amplitude, until, when they reach the melting point, 

 they oscillate so far as to go far over, and then they revolve. So I 

 propound the hypothesis that in liquids the atoms are all the time 

 rotating. They roll around one another, and are easily moved. Now, 

 in the freezing of water, there is what I may call a paradox ; that the 

 point of greatest density is not the freezing point. To explain that, 

 we have simply to suppose that the center of oscillation is not in the 

 middle of the molecule, but that it is eccentric ; that it is the least 

 eccentric at forty degeees, the point of greatest density, but becomes 

 more eccentric both below and above that temperature ; for the more 

 eccentric it is the more space will be required either for oscillation or 

 for revolution. When we freeze water the rotation becomes slower 

 as it cools, until, at thirty-two degrees, there is not force enough to 

 carry it over any more, and then, like a revolving pendulum, it ceases 

 to go over, and oscillates. As it becomes colder the oscillation 

 becomes less ; and, at -460° Fahrenheit, it ceases altogether. 



