Fuly 28, 1870] 
NATURE 
255 
so many liying germs that if uniformly diffused through the pint 
of air, not a thimbleful could be taken without containing several. 
These germs, placed under fayourable circumstances, would soon 
grow large enough to be detected without any difheulty, 
rer» be LIONEL 5, BEALE 
The Source of Solar Energy 
Ir is, I think, rather unfortunate that Mr. Proctor, in his 
recent work entitled ‘‘ More Worlds than One,” should have 
re-advocated the earlier and now discarded views of Sir W. 
Thomson concerning the source of solar heat or energy by 
meteoric percussion. ‘That theory, however ingenious as advanced 
by the physicist, is surely hardly one to be admitted by the 
astronomer, Nothing less than an intense desire or necessity for 
finding some solution to the problem, whence or how the solar 
heat is maintained, could have encouraged scientific men seriously 
to adyance or support so plausible and unsatisfactory a doctrine, 
or one, when examined, so little supported by what we really 
kmow either of meteors or of nature’s laws. Having given much 
attention to meteoric astronomy, may I be permitted briefly to 
state what I hold are ‘serious and practical objections to the 
validity of the meteoric or dynamical theory as applied to the 
conseryation of solar heat and energy. 
1. Because meteors and aérolites are known to impinge and 
strike the earth in her orbit, evga, as I understand Mr. Proctor, 
numbers infinitely greater must no doubt be constantly rushing 
into the sun, as a body at once far larger, and much nearer to 
myriads of such bodies than the earth herself ; but which, at a 
much smaller distance, are more likely to be diawn into the sun. 
Now, all that we really do know about meteors amounts to this, 
that by far the greater number of shooting stars visible in our 
atmosphere, in size no larger than a bean, and really separated 
from each other by thousands of miles, belong to fixed and 
definite systems or rings, having fixed radiant points for certain 
epochs or periods, showing clearly that these bodies are revolving 
round the sun, in courses as true and regular as the planets 
themselves, and are no more eddying or rushing into the sun, 
merely because they are so insignificant, than is the earth herself, 
Haying projected upon celestial charts the apparent courses or 
tracks of nearly 5,000 meteors, observed during every part of the 
year, I feel I am justified in stating that not more than seven or 
eight per cent. of the shooting stars observed on any clear night 
throughout the year, are sforadic, or do not belong to meteor 
systems at present known to us, More than one hundred meteor 
systems are now recognised, several of which appear most cer- 
tainly to be connected with known comets ; and from a paper J 
haye just received from Professor Schiaparelli, of Milan, it 
would appear that the approximate average fevvhe/ion distance 
for 44 of these meteor systems is not less than 0°7, the earth’s 
distance from the sun being 1°0 ; whilst of these 44 systems, only 
4, or about Io per cent. have their Aerthelion distance under 0'1, 
that is, approach the sun nearer than nine millions of miles ! 
Now, it is pretty well admitted that meteors are intimately con- 
nected with comet systems, yet out of some 200 comets, the ele- 
ments of whose orbits have been calculated with tolerable pre- 
cision, only 5 per cent. have their feriie/ion distance under Q'I, 
The same argument holds good also for planets, whose numbers 
also diminish after a certain considerable mean distance from the 
sun. Are these facts, then, in accordance with the notion that 
meteoric bodies either increase in number as we approach the 
sun, or that meteors are so constantly losing their senses, or sense 
of gravity, as to be ever rushing into or against the sun? I might 
almost ask, do azy meteors rush or fall into the sun? Is it 
probable that the mass of all ‘‘the countless myriads of meteors” 
in the solar system exceeds that of a single planet? whether 
that of Mercury or Jupiter does not much signify. When we take 
into consideration the gigantic amount of meteoric deposits re- 
quired to maintain the solar heat for hundreds of millions of 
years, in the meteoric theory, surely the supply of meteors would 
long since haye been exhausted, were the supply at least con- 
fined merely to the meteors under a mean distance of o'r belong- 
ing to our own solar system! The argument, to begin with, is 
in a great degree fallacious, ¢,g, because meteors frequently 
strike the earth, they must, it is argued, strilse the sun in yastly 
greater numbers, and with far greater velocities. But it is for- 
gotten that the meteors themselyes, like the earth, are revolying 
round the sun asa common centre, in regular orbits, and only 
by accident, as it were, come into mutual collision, just as the 
tail of acomet might pass through the system of Jupiter and his 
satellites ; while to the end of time neither the earth nor the 
meteors need necessarily come into contact with the sun, 
2, But it is not merely meteors belonging to the solar system 
which are taxed to provide fuel for our sun ; sface itself may be 
filled with meteors ready to impinge upon the sun. ‘The argu- 
ments against this are; (1) judging from analogy as well as from 
facts, comparatively few meteors are s/oradic, consequently the 
majority cannot belong to stellar space, but to our own system ; 
(2) granting that space itself is really more or Jess filled with 
meteors, these would not necessarily rush straight into the sun, 
unless, as would very unlikely be the case, they had no proper 
motion of their own. They might be drawn into or enter our 
system, it is true, but, according to Schiaparelli, only to circu’ate 
like comets in definite orbits, 
3, The zodiacal /ight is another victim to the emergencies of 
the meteoric theory of solar energy. Whethre composed of 
myriads of small meteors, or merely a nebulous appendage, or 
atmospheric emanation belonging to the sun, is it credible that 
for hundreds of millions of years there could, physically speak- 
ing, be sufficient material in the zodiacal light to maintain the 
sun’s heat and supply all the fuel required? Has it ever yet 
been proved that the entire mass of matter constituting the 
zodiacal light, is either composed of‘matter ina solid state, or, if 
it were, that its mass would be equal to that of our own earth? 
if composed of separate meteors, are they not each individually 
revolving round the sun, rather than occupied in being gradually 
drawn into it as a yortex ? * 
Of course I do not say that meteors are wever drawn into 
the sun, or that they may not occasionally ani by accident 
enter the solar atmosphere; I have merely endeavoured to 
show that, from what we really do know about meteors 
and the laws of nature, it is highly improbable that our sun 
could derive, in sufficient quantity, a needful supply of fuel 
from meteoric sources, The comet of 1843, which approached 
the sun within 550,coo miles, was not sensibly deflected 
from its course; it is just possible that so small a thing as an 
aérolite might at that distance have been drawn into the sun ; 
but is it not also possible, from what we know of comet and 
meteor systems, it may be wisely ordained that the smaller bodies 
of our solar system, such as meteors, do not as a rule approach 
the sun too closely ; and they probably do not, if their feré- 
helia distances are rarely under 10,000,000 of miles ? 
Aérolites ave doubtless of larger size and weight than shooting 
stars, and, as far as is yet known, not so regular in their appear- 
ance as shooting stars ; but even with that class of phenomena, 
we notice a certain degree of periodicity in maxima and minima 
for certain times of the year, tending to show that they also may be 
subject to regular laws, and not fall so frequently or promis- 
cuously upon the sun’s surface as has been sometimes supposed. 
If they do not fall in vastly greater numbers, area for area, upon 
the sun than they do upon our earth, certainly the dynamical 
effect would be very minute! I may here also observe that even 
these bodies generally fall to the earth without being consumed, 
and with a very moderate velocity ; their original cosmical yelo- 
city having been lost before reaching the surface of the earth. 
In the case of an aérolite falling upon the sun’s surface, its origi- 
nal yelocity may similarly have been gradually checked in its 
passage through the solar atmosphere, and a considerable amount 
therefore of the calculated mechanical effect lost. Small meteors 
would probably be consumed thousands of miles from the real 
body of the sun, seeing that the sun’s inflamed atmosphere is 
now known to extend at times some 50,000 miles. It might 
almost be a question whether the sun’s proper heat may not even 
be greater than that caused by the simple friction of a meteor 
through the solar atmosphere ! 
I merely allude to these minor matters, however, in order to 
point out some of the numerous uncertainties and difficulties con- 
nected with this meteoric or mechanical theory of the origin and 
conservation of solar heat, in addition to those already alluded 
to, bearing more especially upon the astronomical bearings of 
the question. For the present it must still remain a mystery, 
whence or how the solar heat is maintained, or to what extent 
really wasted. 
Prestwich, Manchester, July 11 Robert P. GreG 
Choice of a Microscope 
WirH all respect to the judgment of my friend Mr, Ray 
Lankester, I should like to be allowed to oppose a few of the 
statements made by him in his remarks on the Choice of a 
* We beg to refer our readers to Jones’ and Liais’ observations of the 
Zodiacal Light, They certainly haye not received the attention in this 
country that they deserve.—Eb. 
