442 
is not contained in our atmosphere in any appreciable 
quantity. j 
Further proof of the fact that stellar space is filled 
with gaseous matter is furnished by spectrum analysis, 
and it appears from recent investigation, by Dr. Huggins 
and others, that the nucleus of a comet contains very 
much the same gases found occluded in meteorolites, 
including “carbon, hydrogen, nitrogen, and probably 
oxygen,’’ whilst according to the views set forth by Dewar 
and Liveing it also contains nitrogenous compounds such 
as cyanogen. 
Adversely to the assumption that interplanetary space 
is filled with gases, it is urged that the presence of ordi- 
nary matter would cause sensible retardation of planetary 
motion, such as must have made itself felt before this ; 
but assuming that the matter filling space is an almost 
perfect fluid not limited by border surfaces, it can be 
shown on purely mechanical grounds, that the retardation 
_ by friction through such an attenuated medium would be 
very slight indeed, even at planetary velocities. 
But it may be contended that, if the views here advo- 
cated regarding the distribution of gases were true, the 
sun should draw to itself the bulk of the least diffusible, 
and therefore the heaviest gases, such as carbonic anhy- 
dride, carbonic oxide, oxygen and nitrogen, whereas 
‘spectrum analysis has proved on the contrary a prevalence 
of hydrogen. 
In explanation of this seeming anomaly, it can be 
shown in the first place, that the temperature of the sun 
is so high, that such compound gases as carbonic anhy- 
dride and carbonic oxide, could not exist within it, their 
point of dissociation being very much below the solar 
temperature ; it has been contended, indeed, by Mr. 
Lockyer, that none of the metalloids have any existence 
at these temperatures, although, as regards oxygen, 
Dr. Draper asserts its existence in the solar photosphere ; 
there must be regions, however, outside that thermal 
limit, where their existence would not be jeopardised by 
heat, and here great accumulation of these comparatively 
heavy gases that constitute our atmosphere would pro- 
bably take place, were it not for a certain counterbalancing 
action. 
I here approach a point of principal importance in my 
argument, upon the proof of which my further conclusions 
must depend. 
The sun completes one revolution on its axis in 25 
days, and its diameter being taken at 882,000 miles, 
it follows that the tangential velocity amounts to 1°25 
miles per second, or to 441 times the tangential velocity 
of our earth. This high rotative velocity of the sun must 
cause an equatorial rise of the solar atmosphere to which 
Mairan, in 1731, attributed the appearance of zodiacal 
light. La Place rejected this explanation on the ground 
that the zodiacal light extended to a distance from the 
sun exceeding our own distance, whereas the equatorial 
rise of the solar atmosphere due to its rotation could not 
exceed 9-20ths of the distance of Mercury. But it must 
be remembered that. La Place based his calculation upon 
the hypothesis of an empty stellar space (filled only with 
an imaginary ether), and that the result of solar rotation 
would be widely different, if it wassupposed to take place 
within a medium of unbounded extension. In this case 
pressures would be balanced all round, and the sun 
would act mechanically upon the floating matter sur- 
rounding it in the manner of a fan, drawing it towards 
itself upon the solar surfaces, and projecting it outwards 
in a continuous disk-like steam. 
By this fan action, hydrogen, hydrocarbons, and oxygen, 
are supposed to be drawn in enormous quantities toward 
the polar surfaces of the sun; during their gradual 
approach, they will pass from their condition of extreme 
attenuation and extreme cold, to that of compression, 
accompanied with rise of temperature, until on approach- 
ing the photosphere, they burst into flame, giving rise to a 
| NATURE. = 
[March 9, 1882 
great development of heat, and a temperature commen- 
surate with their point of dissociation at the solar density. 
The result of their combustion will be aqueous vapour 
and carbonic anhydride or oxide, according to the 
sufficiency or insufficiency of oxygen present to complete 
the combustion, and these products of combustion in 
yielding to the influence of centrifugal force will flow 
towards the solar equator, and be thence projected into 
space, 
The next question for consideration is: What would 
become of these products of combustion when thus ren- 
dered back into space? Apparently they would gradually 
change the condition of stellar material, rendering it more 
and more neutral, but I venture to suggest the possibility, 
nay, the probability, that solar radiation would, under 
these circumstances, step in to bring back the combined 
materials to a condition of separation by a process of 
dissociation carried into effect at the expense of that solar 
energy which is now supposed to be lost to our planetary 
system. 
According to the law of dissociation as developed by 
Bunsen and Sainte-Claire Deville, the point of dissociation 
of different compounds depends upon the temperature on 
the one hand, and upon the pressure on the other. Ac- 
cording to Sainte-Claire Deville, the dissociation tension 
of aqueous vapour of atmospheric pressure and at 2800° C. 
is 0.5, or only half of the vapour can exist as such, its 
remaining half being found as a mechanical mixture of 
hydrogen and oxygen, but that with the pressure, the 
temperature of dissociation rises and falls, as the tem- 
rerature of saturated steam rises and falls with its pressure. 
It is therefore conceivable that the temperature of the 
solar photosphere may be raised by combustion to a tem- 
perature exceeding 2800° C., whereas dissociation may be 
effected in space at a lower temperature. 
But these investigations had reference only to heats 
measured by means of pyrometers, but do not extend to 
the effects of radiant heat. Dr. Tyndall has shown by his 
exhaustive researches that vapour of water and other 
gaseous compounds intercept radiant heat in a most re- 
markable degree, and there is other evidence to show that 
radiant energy from a scource of high intensity possesses 
a dissociating power far surpassing the measurable tem- 
perature to which the compound substance under its 
influence is raised. Thus carbonic anhydride and water 
are dissociated in the leaf cells of plants, under the 
influence of the direct solar ray at ordinary summer tem- 
perature, and experiments in which I have been engaged 
for nearly three years! go to prove that this dissociating 
action is obtained also under the radiant influence of the 
electric arc, although it is scarcely perceptible if the 
source of radiant energy is such as can be produced by 
the combustion of oil or gas. 
The point of dissociation of aqueous vapour and car- 
bonic anhydride admits, however, of being determined 
by direct experiment. It engaged my attention some 
years ago, but I have hesitated to publish the qualitative 
results I then obtained, in the hope of attaining to quan- 
titative proofs. 
These experiments consistel in the employment of 
glass tubes, furnished with platinum electrodes, and filled 
with aqueous vapour or with carbonic anhydride in the 
usual manner, the latter being furnished with caustic soda 
to regulate the vapour pressure by heating. Upon im- 
mersing one end of the tube charged with aqueous vapour 
in a refrigerating mixture of ice and chloride of calcium, 
its temperature at that end was reduced to 32° C., cor- 
responding to a vapour pressure, according to Regnault, 
of 1-1800 of an atmosphere. When so cooled no slow 
electric discharge took place on connecting the two elec- 
trodes with a small induction coil. I then exposed the 
1 See Proceedings, Roy. Soc. Vol. xxx. 1 Mar. 1880 and a paper read before 
Section A of the British Association x Sep. 1881 and ordered to be printed in 
the Report. 
