4,000 billion kilogrammes per second, or a mass equal to that of our
moon bi-annually. But so large an addition to the gravitating power of
the sun would quickly become sensible in the movement of the bodies
dependent upon him. Their revolutions would be notably accelerated.
Mayer admitted that each year would be shorter than the previous one by
a not insignificant fraction of a second, and postulated an unceasing
waste of substance, such as Newton had supposed must accompany emission
of the material corpuscles of light, to neutralise continual
reinforcement.

Mayer's views obtained a very small share of publicity, and owned Mr.
Waterston as their independent author in this country. The meteoric, or
"dynamical," theory of solar sustentation was expounded by him before
the British Association in 1853. It was developed with his usual ability
by Lord Kelvin, in the following year. The inflow of meteorites, he
remarked, "is the only one of all conceivable causes of solar heat which
we know to exist from independent evidence."[1154] We know it to exist,
but we now also know it to be entirely insufficient. The supplies
presumed to be contained in the zodiacal light would be quickly
exhausted; a constant inflow from space would be needed to meet the
demand. But if moving bodies were drawn into the sun at anything like
the required rate, the air, even out here at ninety-three millions of
miles distance, would be thick with them; the earth would be red-hot
from their impacts;[1155] geological deposits would be largely
meteoric;[1156] to say nothing of the effects on the mechanism of the
heavens. Lord Kelvin himself urged the inadmissibility of the
"extra-planetary" theory of meteoric supply on the very tangible ground
that, if it were true, the year would be shorter now, actually by six
weeks, than at the opening of the Christian era. The "intra-planetary"
supply, however, is too scanty to be anything more than a temporary
makeshift.

The meteoric hypothesis was naturally extended from the maintenance of
the sun's heat to the formation of the bodies circling round him. The
earth--no less doubtless than the other planets--is still growing.
Cosmical matter in the shape of falling stars and aerolites, to the
amount, adopting Professor Newton's estimate, of 100 tons daily, is
swept up by it as it pursues its orbital round. Inevitably the idea
suggested itself that this process of appropriation gives the key to the
life-history of