534 
consequences. The meteors, in the first place, are not the fuel 
of the sun. We can measure and compute within certain limits 
of error the radiant energy emitted by the sun. The meteoroids 
large enough to give shooting-stars visible to the naked eye are 
scattered very irregularly through the space which the earth 
traverses ; but in the mean each is distant two or three hundred 
miles from its near neighbours. If these meteoroids supply the 
sun’s radiant energy, a simple computation shows that the aver- 
age shooting-star ought to have a mass enormously greater than 
is obtained from the most prolific stone-fall. 
Moreover, if these meteoroids are the source of the solar heat, 
their direct effect upon the earth’s heat by their impact upon our 
atmosphere ought also to be very great: whereas the November 
star-showers, in some of which a month’s supply of meteoroids 
was received in a few hours, do not appear to have been fol- 
lowed by noticeable increase of heat in the air. 
Again, the meteoroids do not cause the acceleration of the 
moon’s mean motion. In various ways the meteors do shorten 
the month as measured by the day. By falling on the earth and 
on the moon they increase the masses of both, and so make the 
moon move faster. They check the moon’s motion, and so, 
bringing it nearer to the earth, shorten the month. They load 
the earth with matter which has no momentum of rotation, and 
so lengthen the day. The amount of matter that must fall upon 
the earth in order to produce in all these ways the observed ac- 
celeration of the-moon’s motion, has been computed by Prof. 
Oppolzer. But his result would require for each meteoroid an 
enormous mass, one far too great to be accepted as possible. 
Again, the supposed power of such small bodies,—bodies so 
scattered as these are, even in the densest streams,—to brea 
up the comets or other heavenly bodies, and also their power, 
by intercepting the sun’s rays, to affect our weather, must, in 
absence of direct proof to the contrary, be regarded as insignifi- 
cant. So, too, their effect in producing geologic changes by 
adding to the earth’s strata has, without doubt, been very much 
over-estimated. During a million of years, at the present rate 
of, say, 15,000,000 of meteors per day, there comes into the air 
about one shooting-star or meteor for each square foot of the 
earth’s surface, 
To assume a sufficient abundance of meteors in ages past to 
accomplish any of these purposes is, to say the least, to reason 
from hypothetical and not from known causes. The same may 
be said of the suggestion that the mountains of the moon are 
due to the impact of meteorites. Enormously large meteoroids 
in ages past must be arbitrarily assumed, and, in addition, a 
very peculiar plastic condition of the lunar substance, in order 
that the impact of a meteoroid can make in the moon depres- 
sions ten, or fifty, or a hundred miles in diameter, surrounded 
by abrupt mountain walls two, and three, and four miles high, 
and yet the mountain walls not sink down again. 
The known visible meteors are not large enough nor numerous 
enough to do the various kinds of work which I have named. 
May we not assume that an enormous number of exceedingly 
small meteoroids are floating in space, are falling into the sun, 
are coming into our air, are swept up by the moon ? May we 
not assume that some of these various results, which cannot be 
due to meteoroids large enough for us to see as they enter the 
air, may be due to this finer impalpable cosmic dust? Yes, we 
may make such an assumption. There exist, no doubt, multi- 
tudes of these minute particles travelling in space. But science 
asks not only for a true cause, but a sufficient cause. There 
must be enough of this matter to do the work assigned to it. At 
present we have no evidence that the total existing quantity of 
such fine material is very large. It is to be hoped that through 
the collection and examination of meteoric dust we may soon 
learn something about the amount which our earth receives 
Until that shall be learned, we can reason only in general 
terms. So much matter coming into our atmosphere as these 
several hypotheses require would, without doubt, make its 
presence known to us in the appearance of our sunset skies and 
In a far greater deposit of meteoric dust than has ever yet been 
proven. 
A meteoroid origin has been assigned to the light of the solar 
corona. It is not unreasonable to suppose that the amount of 
the meteoroid matter should increase toward the sun, and that 
the illumination of such matter would be much greater near the 
solar surface. But it is difficult to explain upon such an hypo- 
thesis the radial structure, the rifts, and the shape of the curved 
lines, that are marked features of the corona. These seem to be 
inconsistent with any conceivable arrangement of meteoroids in 
NATURE 
[ Sef. 30, 188 
the vicinity of the sun. If the meteoroids are arranged 
random, there should be a uniform shading away of light as w 
go from the sun. If the meteoroids are in streams along 
cometary orbits, all lines bounding the light and shade in th 
coronal light should evidently bz projections of conic sections o| 
which the sun’s centre is the focus. There are curved lines in 
abundance in the coronal light, but, as figured by observers ani 
in the photographs, they seem to be entirely unlike such projec 
tions of conic sections. Only by a violent treatment of the 
observations can the curves be made to represent such projec 
tions. They look as though they were due to forces at the sun’s 
surface rather than at his centre. If those complicated line: 
have any meteoroid origin (which seems very unlikely), they 
suggest the phenomena of comets’ tails rather than meteoroid 
streams or sporadic meteors. The hypothesis that the long rays 
of light which sometimes have been seen to extend several 
degrees from the sun at the time of the solar eclipse are meteor 
streams seen edgewise, seems possibly true, but not at all 
probable. ] 
The observed life of the meteor is only a second, or at most a 
few seconds, except when a large one sends down stones to 
remain with us. What can we learn about its history an 
origin? 
Near the beginning of this century, when small meteors were 
looked on as some form of electricity, the meteorites were very 
generally regarded as having been thrown out from the lunar 
volcanoes. But as the conviction gained place that the meteor- 
ites moved not about the earth, but about the sun, it was seen 
that the lunar volcanoes must have been very active to have sent 
out such an enormous number of stones as are needed, in order 
that we should so frequently encounter them. When it was 
further considered that there is no proof that lunar volcanoes are 
now active, and that when they were active they were more 
likely to have been open seas of lava, not well fitted to shoot 
out such masses, the idea of the lunar origin of the meteorites 
gradually lost ground. 
But the unity of meteorites with shooting-stars, if true, in- 
creases a hundredfold the difficulty, and would require that the 
comets have the same origin with the meteorites. No one 
claims that the comets came from the moon. 
That the meteorites came from the earth’s volcanoes is still 
held by some men of science, particularly by the distinguished 
Astronomer-Royal for Ireland. The ditficulties of the hypo- 
thesis are, however, exceedingly great. In the first place, th 
meteorites are not like terrestrial rocks. Some minerals in 
them are like minerals in the rocks. Some irons are like the 
Greenland terrestrial irons. But no rock in the earth has yet 
been found that would be mistaken for a meteorite of any one of 
the two or three hundred known stone-falls. The meteorites 
resemble the deep terrestrial rocks in some particulars, it is true, 
but the two are also thoroughly unlike. 
The terrestrial voleanoes must also have been wonderfully 
active to have sent out such a multitude of meteorites as will 
explain the number of stone-falls which we know, and which we 
have good reason to believe, have occurred. The volcanoes 
must also have been wonderfully potent. The meteorites come 
to us with planetary velocities. In traversing the thin upper air 
they are burned and broken by the resisting medium. Long 
before they have gone through the tenth part of the atmosphere 
the meteorites usually are arrested and fall to the ground. If 
these bodies were sent out from the earth’s volcanoes, they left 
the upper air with the same velocity with which they now return 
to it. What energy must have been given to the meteorite 
before it left the volcano, to make it traverse the whole of our’ 
atmosphere and go away from the earth with a planetary 
velocity. Is it reasonable to believe that volcanoes were ever so 
potent, or that the meteorites would have survived such a 
journey ? 
No one claims that the meteors of the star-showers, or their 
accompanying comet, came from the earth’s volcanoes. To 
ascribe:a terrestrial origin to meteorites is, then, to deny the 
relationship of the shooting-star and the stone-meteor. Every 
reason for their likeness is an argument against the terrestrial 
origin of the stones. To suppose that the meteors came from 
any planets that have atmospheres involves difficulties not unlike 
to, and equally serious with, those involved in the theory of a 
terrestrial origin. 
The solar origin of meteorites has been seriously urged, and 
deserves a serious answer. The first difficulty which this hypo- 
thesis meets is that solid bodies should come from the hot sun. 
