Only one external source can be named: the falling of meteors into the sun must yield some heat just as a shooting star yields some heat to our atmosphere, but the question is whether the quantity of heat obtainable from the shooting stars is at all adequate for the purpose.
The ordinary shooting stars vary from the brilliancy of a firstto a sixth-magnitude star.
On a clear moonless night one person may count eight or ten shooting stars in an hour.
The finer meteors on entering the air only weigh a few hundred or, at most, a few thousand pounds, while the smallest shooting stars visible to the eye may probably be equal in size to coarse grains of sand, and still be large enough to evolve all the light presented by them.
Quetelet's astronomical papers refer chiefly to shooting stars and similar phenomena.