March 9, 1882 | | 
NATURE 
443 
end of the tube projecting out of the freezing mixture, 
backed by white paper, to solar radiation (on a clear 
summer’s day) for several hours, when upon again con- 
necting up to the inductorium, a discharge, apparently 
that of a hydrogen vacuum, was obtained. This experi- 
ment being repeated furnished unmistakable evidence, I 
thought, that aqueous vapour had been dissociated by 
exposure to solar radiation. The CO, tubes gave, how- 
ever, less reliable results. Not satisfied with these quali- 
tative results, I made arrangements to collect the perma- 
ent gasesso produced by means of a Sprengel pump, 
but was prevented by lack of time from pursuing the 
inquiry, which I purpose, however, to resume shortly, 
being of opinion that, independently of my present 
speculation, the experiments may prove useful in extend- 
ing our knowledge regarding the laws of dissociation. 
Assuming, for my present purpose, that dissociation of 
aqueous vapour was really effected in the experiment just 
described, and assuming, further, that stellar space is 
filled with aqueous and other vapour of a density not ex- 
ceeding the 1-2000th part of our atmosphere, it seems rea- 
sonable to suppose that its dissociation would be effected 
by solar radiation, and that solar energy would thus be 
utilised. The presence of carbonic anhydride and car- 
_bonic oxide would only serve to facilitate the decomposi- 
tion of the aqueous vapour by furnishing substances to 
combine with nascent. oxygen and hydrogen. By means 
of the fan-like action resulting from the rotation of the 
sun, the vapour dissociated in space to-day would be 
drawn towards the polar surfaces of the sun to-morrow, 
be heated by increase in density, and would burst into 
flame at a point where both their density and tempera- 
ture had reached the necessary elevation to induce com- 
bustion, each complete cycle taking, however, years to be 
accomplished. The resulting aqueous vapour, carbonic 
anhydride and carbonic oxide, would be drawn towards 
the equatorial regions, and be then agaln projected into 
space by centrifugal force. 
Space would, according to these views, be filled with 
gaseous compounds in process of decomposition by solar 
radiant energy, and the existence of these gases would 
furnish an explanation of the solar absorption spectrum, 
in which the lines of some of the substances may be 
entirely neutralised and lost to observation. As regards 
the heavy metallic vapours revealed in the sun by the 
spectroscope, it is assumed that these form a lower and 
denser solar atmosphere, not participating in the fan-like 
action which is supposed to effect the light outer 
atmosphere only, in which hydrogen is the principal factor. 
Such a dense metallic atmosphere could not participate 
in the fan action affecting the lighter photosphere, because 
this is only feasible on the supposition that the density of 
the in-flowing current is, at equal distances from the 
gravitating centre, equal or nearly equal to the outflowing 
current. It is true that the products of combustion of 
hydrogen and carbonic oxide are denser than their 
constituents, but this difference may be balanced by their 
superior temperature on leaving the sun, whereas the 
metallic vapours would be unbalanced, and would there- 
fore obey the laws of gravitation, recalling them to the 
sun. On the surface of contact between the two solar 
atmospheres, intermixture induced by friction, must take 
place, however, giving rise perhaps to those vortices and 
explosive effects which are revealed to us by the telescope, 
and have been commented on by Sir John Herschel and 
other astronomers. Some of the denser vapours would 
probably get intermixed and carried away mechanically by 
the lighter gases, and give rise to that cosmic dust which 
is observed to fall upon our earth in not inappreciable 
quantities. Excessive intermixture would be prevented 
by the intermediary neutral atmosphere, the penumbra. 
As the whole solar system moves through space at a 
pace estimated at 150,000,000 of miles annually (being 
about one-fourth of the velocity of the earth in its orbit), 
it appears possible that the condition of the gaseous fuel 
supplying the sun may vary according to its state of 
previous decomposition, in which other heavenly bodies 
may have taken part. May it not be owing to such 
differences in the quality of the fuel supplied that the 
observed variations of the solar heat may depend? and may 
it not be in consequence of such changes in the thermal 
condition of the photosphere that sun-spots are formed ? 
The views here advocated could not be thought ac- 
ceptable unless they furnished at any rate a consistent 
explanation of the still somewhat mysterious phenomena 
of the zodiacal light and of comets. Regarding the former, 
we should beable to return to Mairan’s views, the objection 
by La Place being met by a continuous outward flow from 
the solar equator. Luminosity would be attributable to 
particles of dust emitting light reflected from the sun, or 
by phosphorescence. But there is another cause for 
luminosity of these particles, which may deserve a passing 
consideration. Each particle would be electrified by 
gaseous friction in its acceleration, and its electric tension 
would be vastly increased in its forcible removal, in the 
same way as the fine dust of the desert has been observed 
by Werner Siemens to be in a state of high electrification 
on the apex of the Cheops Pyramid. Would not the 
zodiacal light also find explanation by slow electric dis- 
charge backward from the dust towards the sun? and 
would the same cause not account for a great difference 
of potential between the sun and earth, which latter may 
be supposed to be washed by the solar radial current ? 
May not the presence of the current also furnish us with 
an explanation of the fact that hydrogen, while abounding 
apparently in space, is practically absentin our atmosphere, 
where aqueous vapour, which may be partly derived from 
the sun, takes its place? An action analogous to this, 
though on a much smaller scale, may be set up also by 
terrestrial rotation giving rise to an electrical discharge 
from the outgoing equatorial stream to the polar regions, 
where the atmosphere to be pierced by the return flood is 
of least resistance. 
It is also important to show how the phenomena of 
comets could be harmonised with the views here advo- 
cated, and I venture to hope that these occasional visi- 
tors will serve to furnish us with positive evidence in my 
favour. Astronomical physicists tell us that the nucleus 
of a comet consists of an aggregation of stones similar 
to meteoric stones. Adopting this view, and assuming 
that the stones have absorbed in stellar space gases to 
the amount of six times their volume, taken at atmo- 
spheric pressure, what, it may be asked, will be the effect 
of such a mass of stone advancing towards the sun at a 
velocity reaching in perihelion the prodigious rate of 366 
miles per second (as observed in the comet of 1845), 
being twenty-three times our orbital rate of motion? It 
appears evident that the entry of sucha divided mass into 
a comparatively dense atmosphere must be accompanied 
by a rise of temperature by frictional resistance, aided by 
attractive condensation. At a certain point the increase 
of temperature must cause ignition, and the heat thus 
produced must drive out the occluded gases, which in an 
atmosphere 3000 times less dense than that of our earth 
would produce 6X 3000=18,000 times the volume of the 
stones themselves. These gases would issue forth in all 
directions, but would remain unobserved except in that of 
motion, in which they would meet the interplanetary atmo- 
sphere with the compound velocity and form a zone of 
intense combustion, such as Dr. Huggins has lately ob- 
served to surround the one side of nucleus, evidently the 
side of forward motion. The nucleus would thus emit 
original light, whereas the tail may be supposed to consist 
of stellar dust rendered luminous by reflex action pro- 
duced by the light of the sun and comet combined, as 
foreshadowed already by Tyndall, Tate, and others, 
starting each from different assumptions. 
These are in brief the outlines of my reflections regard- 
