No. 5.

On the Age of the Sun's Heat.

Mr. Crol's hypothesis in "Climate and Time," of the possible development of the heat of the sun by the impact and complete coalescence of two bodies, having a very high velocity in space, is open to two objections.

First, considering the sparse distribution of masses in space, the probability of a collision largely depends on their mutual attractions bringing bodies together. With such an enormous proper motion, the effect of this attraction would be so much lessened as to render a collision in the highest degree improbable. Secondly, it assumes an original proper motion of at least thirty times the energy of that possessed by the average star.

There is, however, another hypothesis—that of partial impact, which I have already shewn to be of such probability with bodies having an original proper motion, as to be almost a "vera causa," and which I have also shewn possesses considerable powers in producing many well known cosmical phenomena. The partial impact of two bodies offers an intermediate position between complete collision on the one hand, and mere mutual disturbance on the other. It is the general case of collision, of which complete coalescence is the extreme case. The temperature, which may be developed in a case of partial coalescence, is quite independent of the mass of the sun (nebula) produced, nor will original proper motion of necessity materially influence the result as regards temperature. In all cases of partial impact we have the two escaping bodies and the parts of both which come into collision and coalesce. Proper motion is of importance in causing the escape of the two bodies, which the increased attraction of the coalesced mass tends to prevent.

The temperature of a sun struck off from two larger bodies will depend upon—1st, the original temperature; secondly, the velocity during impact of those parts which come into collision; and thirdly, the chemical composition. The velocity will depend, 1st, upon the original proper motion; 2ndly, upon the mass of the two bodies; 3rdly, upon the distance of the centre of the two bodies at impact; and 4thly, it will be influenced by the amount of distortion produced by attraction, But it will be quite independent of the mass of the sun produced.

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There is thus no limit to the amount of heat a sun may possess at birth, but there is a limit in view of its possible continuance, for, as I have shewn in my letters on temporary stars, the temperature of the coalesced mass may be great enough to project every particle of it entirely into space. The possible temperature of a permanent sun has thus a limit. What this limit is, it is difficult to say, for radiation and chemical composition will in flaence the probable escape of the molecules of a mixed gaseous mass. One thing, however appears certain, that as far as the possibility of the amount of heat that might be generated is concerned, it is practically without limit. The question of the escape of the coalesced bodies, and their peculiarities, I will describe in another letter.