320 
Probable Origin and Age of the Sun. 
[July, 
condensation on cooling took place, a spherical mass like 
that of the sun would result. It is perfectly true that two 
such bodies could never attain the required amount of velo- 
city by their mutual gravitation towards each other. But 
there is no necessity whatever for supposing that their velo- 
cities were derived from their mutual attraction alone : they 
might have been approaching each other with the required 
velocity wholly independent of gravitation. 
We know nothing whatever regarding the absolute motion 
of bodies in Space ; and, beyond the limited sphere of our 
observation, we know nothing even of their relative motions. 
There may be bodies moving in relation to our system with 
inconceivable velocity. For anything that we know to the 
contrary, were one of these bodies to strike our earth the 
shock might be sufficient to generate an amount of heat 
that would dissipate the earth into vapour, though the 
striking body might not be heavier than a cannon-ball. 
There is, however, nothing very extraordinary in the velocity 
which we have found would be required to generate the 
50 million years’ heat in the case of the two supposed bodies. 
A comet having an orbit extending to the path of the planet 
Neptune, approaching so near the sun as to almost graze his 
surface in passing, would have a velocity of about 390 miles 
per second, which is within 86 miles of that required. 
It must be borne in mind, however, that the 476 miles per 
second is the velocity at the moment of collision ; but more 
than one-half of this would be derived from the mutual 
attraction of the two bodies in their approach to each other. 
Suppose, for simplicity of calculation, each body to be equal 
in volume to the sun, and of course one-half the density, 
the amount of velocity which they would acquire by their 
mutual attraction would be 274 miles per second. Conse- 
uently we have to assume an original or projected velocity 
of only 202 miles per second. And if the original velocity 
was 676 per second, the total amount of heat generated 
would suffice for 200 million years at the present rate of 
radiation. 
On former occasions* I expressed it as my opinion that 
the total quantity of heat possessed by the sun could not 
probably exceed 100 million years’ heat. But if we admit 
that the heat was derived from Motion in Space, there really 
does not seem any reason why it may not be double that 
amount. 
It will be asked — Where did the two bodies get their 
motion ? It may as well, however, be asked — Where did 
* Phil. Mag., May, 1868. Climate and Time, chap. 21, 
