j 
= ‘ 
April 27, 1882] 
Dr. Siemens has, in his paper, further suggested that solar 
radiation may effect the dissociation in interstellar space of the 
compounds of oxygen with carbon and with hydrogen, so that 
these elements may reach the sun in an uncombined state, and 
there be burned. He would thus make the sun not ouly a com- 
pressing-engine, but a furnace. While such a dissociation in 
outer space is not impossible, it is to be said that a preliminary 
decomposition, followed by reunion in the solar sphere, would 
in no way augment the ultimate calorific effect of compression 
there. The elements in the act of dissociation in space would 
absorb just as much radiant energy as would be set free by their 
subsequent combination, so that, whether the solar radiations 
are expended in heating or in dissociating the diffused matter, 
the final result in the sun would be the same. It may be further 
remarked, that from what we know of solar chemistry, dis: ocia- 
tion of aqueous vapour and of carbonic dioxide is more likely 
to take place in the sun itself than in the cold regions of outer 
space. 
While, therefore, his suggested addition to the hypothesis 
seems, if not untenable, unnecessary, we are grateful to Dr. 
Siemens for again bringing before us the grand conception which 
dawned upon the mind of Newton, but has found its fuller ex- 
pression in our own day, and, as | have endeavoured to shew in 
the papers already noticed, gives us the elements of a rational 
Physiology of the Universe. T. STERRY Hunt 
Montreal, Canada, April 3 
THE two preceding letters by American men of science of well- 
known position, grant one of the three postulates upon which I 
grounded my solar plan, that of space filled with attenuated 
matter ; they do not object to the second, and all-important one 
of the equatorial outflowing current; Lut they call in question 
the necessity of the third, that of dissociation of attenuated 
matter in space by means of arrested solar energy. Both my 
critics think dissociation in space unnecessary for the main- 
tenance of solar energy, or as Dr. Sterry Hunt very clearly puts 
it: ‘“‘ Whether the solar radiations are expended in Aeating or in 
dissociating the diffused matter, the final result in the sun would 
be the same.” 
I would be disposed to agree with this dictum if taken as an 
abstract proposition, but I do not think that my critics can have 
subjected their view to calculation, the keystone without which 
the arch of speculation cannot te considered as secure. We 
know by experimental evidence that stellar space, and the matter 
filling it, are intensely cold, as proved by the winter-temperature 
of the polar regions ; moreover water exposed even in the tropics 
to free radiation while insulated from the warm earth, freezes to 
a considerable thickness during a single night. 
Let us suppose that the attenuated matter in space has a 
temperature of 160° on the absolute scale (being 114° below the 
freezing-point of water), and that it is 3000 times more rarefied 
than when it reaches by adiabatic comparison the solar photo- 
sphere. The rise of temperature due to this compres ion must 
be according to Rankine’s well-known formula— 
5 ant 
= = "29 — Coens 
a= 71( 2) 7 1632° ahsolute, 
Ai 
and this would make the solar photosphere 1358° on the Centi- 
grade scale ; this temperature is quite inadequate to produce the 
solar luminosity, which must require one equalling, though 
probably not exceeding that of the electric arc. 
But assuming a compression of the attenuated atmosphere up 
to the photospheric density (which according to most authorities 
dees not exceed terrestrial atmospheric density), there would still 
remain the predicament that although a higher maximum tem- 
perature could be reached by compression, very little of the heat 
due to it could be spared for the purpose of radiation, without 
sacrificing the possibility of disposing of the refrigerated gases 
again into space. ‘The refrigerated gases would obey the law of 
solar gravitation to a much greater extent than the heated in- 
coming gases, and would certainly not pass away into space, 
unless acted upon by a considerable extranecus force. The mere 
passage of the solar orb through space at a majestic pace which 
does not exceed one quarter of our orbital velocity, could not 
possibly produce such a result, and ever. the fan action advocated 
in my paper would fail to work in opposition to a large deter- 
mining influence of solar gravitation. 
These conditions are entirely changed if we assume, in addi- 
tion to adiabatic compression and re-expansion, a further source 
NATURE 
693 
of heat such as is produced in combustion. One pound ct 
hydrogen develops in burning about 60,000 heat units, and one 
pound of marsh gas 24,000 heat units ; in my article upon this 
subject, published in the April number of the Winetecnth Century, 
I showed that if only one-twentieth portion of the gases stream- 
ing in upon the polar surfaces at the pace of Ico feet a second 
were combustible gases, they could produce an amount of heat 
more than sufficient to account for the entire solar radiation as 
determined by Herschel and Peuillet. 
There is no reason for supposing that the instreaming gases 
would penetrate beyond the solar photosphere; they would flash 
into combustion whenever their temperature by adiabatic com- 
pression had reached the limit of spontaneous ignition without 
the presence of an igniting solid, a point which, if determined 
experimentally, would give aclue to the real vapour density of 
the photosphere ; and after reaching the point of dissociation, 
combustion would continue in the measure of the abstraction of 
heat by radiation, thus producing a vast accumulation of igneous 
matter of comparatively low density. This would flow on, in 
the manner of a floating body, above the denser gases or vapours 
forming part of the permanent body of the sun, towards the 
equatorial regions, whence it would be propelled into space at a 
temperature exceeding to some extent that of the inflowing gases 
after compression, but before combustion, thus aiding, instead 
of retarding the supposed solar fan action. 
The fan-action itself would be produced, no doubt, at the 
expense of solar rotation ; but, in order to appreciate this re- 
tarding influence at its true value, it must be borne in mind that 
the flow of gases once established has only to be changed in 
direction ; the velocity acquired by the inflowing gases is simply 
transferred to the outflowing current diminished by an amount 
of rotative force sufficient to cover frictional retardation. The 
very interesting leading article in last week’s NATURE, regarding 
the solar observations in America, during the last eclipses, now 
published for the first time, furnishes an unexpected and most 
striking corroboration of the solar fan-action which I had ven- 
tured to put forward as anecessary consequence of solar rotation 
in space filled with attenuated matter. 
I am well aware that my paper read before the Royal Society 
does scant justice to those who have devoted much time ard 
ingenuity to the subject of solar physics, and that, morecver, 
many points of considerable interest connected with the views L 
advocate have been indicated only, instead of having been fully 
developed ; but, on the whole, I thought it was better to present 
my views in mere outline before an audience well acquainted 
with our present information regarding solar physics, and with 
only half an hour's time at their disposal. 
The elaboration of such a subject would necessitate the writing 
of a book rather than of a paper, and perhaps Dr. Sterry Hunt, 
who has already done so much to elucidate our present know- 
ledge of solar physics, may be induced to extend his Jabours in 
this direction. C. W. SIEMENS 
12, Queen Anne’s Gate, Westminster, April 26 
Silurian Fossils in the North-West Highlands 
My friend, Mr. Hudleston, in his letter on the Silurian fossils 
in the North-western Highlands, states very clearly a point 
which at the present time is of the highest importance to all 
students of the metamorphic rocks. If it can be proved that 
the Durness limestone, which contains undoubted lower Silurian 
fossils, is identical with the series in We-tern Sutherland and 
Ross, which Mr. Hudleston terms the quartzo-dolomitic, then 
the so-called ‘*‘ Newer Gneiss”’ must be more recent than it, and 
thus must be a metamorphosed representative of some part of 
the Silurian series. This would prove that very great regional 
metamorphism has taken place in the latter half of the Paleozoic 
period ; and that its mineral condition will not aid us materially 
in determining the age of a rock which has once been stratified. 
But is this identity proved ; and is it certain that the Durness 
limestone is more ancient than the Newer Gneiss series? 1 have 
not myself had the opportunity of investigating the Durness 
region, though I have examined several specimens of its lime- 
stone; and from the condition of these and my knowledge of 
parallel cases, and of metamorphic rocks in general, do not 
hesitate to say that I should require very clear stratigraj hical 
evidence before I could believe the Durness limestone to under- 
lie the ‘‘ Newer Gneiss.” The former is no more metamorphic 
than are several of the Palaeozoic limestones ; the latter is always 
considerably, sometimes rather highly, metamorphosed, But in 
