The sentences on page 193 gave rise to a controversial attack by Mr.
J. C. F. Zoellner, in his book ‘On the Nature of the Comets,’ on Sir
W. Thomson, on which I took occasion to express myself briefly in the
preface to the second part of the German translation of the ‘Handbook
of Theoretical Physics,’ by Thomson and Tait. I give here the passage
in question:--
‘I will mention here a further objection. It refers to the question as
to the possibility that organic germs may occur in meteoric stones,
and be conveyed to the celestial bodies which have been cooled. In
his opening Address at the Meeting of the British Association in
Edinburgh, in August 1871, Sir W. Thomson had described this as “not
unscientific.” Here also, if there is an error, I must confess that I
also am a culprit. I had mentioned the same view as a possible mode
of explaining the transmission of organisms through space, even a
little before Sir W. Thomson, in a lecture delivered in the spring of
the same year at Heidelberg and Cologne, but not published. I cannot
object if anyone considers this hypothesis to be in a high, or even in
the highest, degree improbable. But to me it seems a perfectly correct
scientific procedure, that when all our attempts fail in producing
organisms from inanimate matter, we may inquire whether life has
ever originated at all or not, and whether its germs have not been
transported from one world to another, and have developed themselves
wherever they found a favourable soil.
‘Mr. Zoellner’s so-called physical objections are but of very small
weight. He recalls the history of meteoric stone, and adds (p. xxvi.):
“If, therefore, that meteoric stones covered with organisms had escaped
with a whole skin in the smash-up of its mother-body, and had not
shared the general rise of temperature, it must necessarily have first
passed through the atmosphere of the earth, before it could deliver
itself of its organisms for the purpose of peopling the earth.”
‘Now, in the first place, we know from repeated observations that the
larger meteoric stones only become heated in their outside layer during
their fall through the atmosphere, while the interior is cold, or even
very cold. Hence all germs which there might be in the crevices would
be safe from combustion in the earth’s atmosphere. But even those germs
which were collected on the surface when they reached the highest and
most attenuated layer of the atmosphere would long before have been
blown away by the powerful draught of air, before the stone reached
the denser parts of the gaseous mass, where the compression would be
sufficient to produce an appreciable heat. And, on the other hand, as
far as the impact of two bodies is concerned, as Thomson assumes, the
first consequences would be powerful mechanical motions, and only in
the degree in which this would be destroyed by friction would heat be
produced. We do not know whether that would last for hours, for days,
or for weeks. The fragments, which at the first moment were scattered
with planetary velocity, might escape without any disengagement of
heat. I consider it even not improbable, that a stone, or shower of
stones, flying through the higher regions of the atmosphere of a
celestial body, carries with it a mass of air which contains unburned
germs.
‘As I have already remarked I am not inclined to suggest that all these
possibilities are probabilities. They are questions the existence and
signification of which we must remember, in order that if the case
arise they may be solved by actual observations or by conclusions
therefrom.’