126 - Transactions.=—Miscellaneous, 
after collision any portion will acquire much greater energy than before, we 
may reasonably assume that no part will acquire four times the energy of 
motion, and be thrown off into space, On the other hand, if two bodies 
come into partial collision, a piece of each would coalesce, and the rest 
would pass on into space. Ifthe motion be entirely destroyed, the temperature 
developed by coalescence will be the same, no matter what proportion be 
struck off; whilst, if the pieces struck off be very small, the coalesced mass 
will have but little attractive power to keep the body together, and hence 
the velocity of each particle may be great enough to project the whole into 
space ; whereas we have seen, in the case of complete coalescence, none 
would be able to be thus projected. This is a most important distinction 
between partial and complete collision. 
Influence of Chemical Composition. 
If two bodies, each a mixture of chemical elements, meet and destroy 
their motion of translation, then a molecular motion of identically the 
same energy must be developed (a small part will be converted into some 
form of potential energy, but this we will disregard). If a mass of small 
bodies have the same energy as an equal single mass, the velocity is also 
equal. Whence we must also assume that the velocity of the molecules, 
no matter what may be their respective weights, is not greater than the 
velocity of the whole body was before impact. Therefore, from what has 
been stated, in direct impact no particle will have sufficient velocity to leave 
the mass immediately after impact. But different elements having the same 
velocity are at different temperatures, inversely proportional to their mole- 
cular weight; the heavy atoms are therefore very much hotter than the 
light ones. We know by the laws of heat that these unequal temperatures 
will tend to equality; but it is worth while looking at this a little in detail. 
Let us suppose a hydrogen and a mercury particle to meet. The mercury 
is one hundred times as heavy as hydrogen, but the velocity of both is the 
same. The collision cannot produce heat, as it is heat motion already. 
The principle of energy at once tells us that the mercury will lose a part 
of its velocity, and the velocity of the hydrogen will be increased. Let this 
happen many times, and the temperature will become equal; in other 
words, the hydrogen will be moving ten times as fast as the mercury. Let 
both of these particles come to the surface of the body; their molecular 
motion will cause them to leave it; the hydrogen will probably have velocity 
sufficient to carry it away from effective attraction, which is impossible 
with the mercury, as initially its velocity was insufficient, and now it is less 
than before. Thus we see that at the surface of a mixed gaseous atmo- 
sphere there is a tendency the opposite to that of the diffusion of gases; 
probably the hydrogen and lighter atomic weight elements will be on the out- 
TE UN Inr diee PENES = Ss ae 
