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answer.* He points to the fact, confirmed by numerous ob- 
servers, that the larger meteoric stones, during their transit 
through our atmosphere, become heated only on the outer sur- 
face, the interior remaining cold — often very cold. Grerms 
which may happen to lie in the crevices of such stones would 
be protected from scorching while travelling through the air. 
Those, moreover, which lie on or near the surface of the aerolite 
would, as soon as it entered the upper and and most attenuated 
strata of our atmosphere, be blown off by the swift and violent 
current of air long ere the stone can rend those denser layers of 
our gaseous envelope where compression is sufficiently great to 
cause a perceptible rise of temperature. As regards that other 
point of debate, referred to by Thomson only, the collision 
of two cosmical masses, Helmholtz shows that the first result of 
contact would be violent mechanical movement, and that it is 
only when they begin to be worn down and destroyed by 
friction that heat would be developed. It is not known 
whether this may not continue for hours or days, or even 
weeks. Such portions as at the first moment of contact are 
hurled away with planetary velocity may consequently be 
driven from the scene of action before any rise of temperature 
may have taken place. 46 It is not impossible, 5 ’ he adds, 44 that 
a meteorite or a swarm of meteorites, in traversing the upper 
layers of the almosphere of a heavenly body, may either scatter 
from them or carry with them a quantity of air containing 
unscorched germs. These are possibilities which are not yet to 
be taken as probabilities ; they are questions which, from the 
fact of their existence and range, are to be kept in sight, so that, 
should a case arise, they may receive an answer either by actual 
observations or by some conclusive deduction.” It should be 
mentioned here that these views of Helmholtz’s are also to be 
met with in a supplement to his lecture on the origin of the solai 
system. 
In tracing the gradual development of this important contro- 
versy we now arrive at the present year, and proceed to discuss 
the allusion made to it by Professor Allen Thomson in his 
address at Plymouth. The difficulty regarding the origin 
of life is, he considers, not abolished, but only removed to a 
more remote period, by the supposition of the transport of germs 
from another planet, or their introduction by means of me- 
teorites or meteoric dust; for, besides the objection arising 
from the circumstance that these bodies must have been sub- 
jected to a very high temperature, we should still have every- 
thing to learn as to the way in which the germs arose in the 
* “Handbuch der theoretischen Physik. Von W. Thomson und P. Gr. 
Tait.” Uebersetzung von H. Helmholtz und Gr. Wertheim. Braunschweig : 
Yieweg und Sohn. 1874. Erster Band. Zweiter Theil. 11. 
