164 

NATURE 
[Fune 29, 1871 

like darkened areas ; but, on the contrary, when we con- 
sider the high temperature of the sun, we may conceive 
them to be formed of matter in a glowing state, so that 
products of condensation such as these could scarcely, if 
at all, be perceived on the luminous disc of the sun. On 
the other hand, the author believes that in the cases of the 
great and still warm planets, Jupiter and Saturn, we see 
the sun-illumined aqueous clouds that rise in bright belts 
at the equator. We believe the author’s object is to show 
that, while the visible effects of condensation appear in 
the atmospheres of Jupiter and Saturn, it is only on the 
liquid surface that they are exhibited by the sun, and thus 
its atmosphere remains transparent. 
We have, accordingly, in the equatorial zone and in 
the higher latitudes distinct regions of preponderating 
atmospheric cloudiness, and between them, like the zones 
of the trade winds on the earth, lie areas of relative 
clearness. All this, if I rightly understand the author, 
is not apparent to the observer, but its effects are seen on 
the glowing liquid solar surface, where, beneath the un- 
clouded areas, radiation is more induced than in other 
places, and the formation of sun-spots is the consequence. 
To the foregoing causes of atmospheric disturbance 
must be added the eruptions of hydrogen that are shown 
by the spectroscope. 
On the whole it is the s¢///ness and clearness of certain 
parts of the atmosphere that induce the formation of 
spots ; and, as the final result of his arguments, Prof. 
Zollner sums up as follows :— 
“The sun-spots are slag-like products of a cooling pro- 
cess caused by the radiation of heat from the glowing 
liquid surface, and they dissolve again in consequence of 
disturbances of equilibrium in the atmosphere which are 
brought on by themselves. If these disturbances are not 
merely local, but of more general extent, then, at the times 
of such general atmospheric disturbances, the formation 
of new spots is but little favoured, because the essential 
conditions of a considerable lowering of temperature are 
wanting, namely—s¢c//ness and clearness of the atmo- 
sphere. When the atmosphere, after the dissolution of 
the spots, gradually tranquillises, the process begins anew, 
and it assumes a eriodic character, while the conditions 
of the solar surface are to be regarded as constant in the 
mean. of lengthened periods. The local distribution of the 
spots must, according to this theory, depend on the zones 
of greatest atmospheric clearness, which, as has been 
shown, are generally coincident with the zones of the 
greatest development of the spots.” 
Such, as they appear to me, are Prof. Zdllner’s views of 
the sun’s spots ; and if, as is quite possible, I have not 
everywhere succeeded in comprehending him, I freely 
admit that any misconstruction I have made may 
be attributable to my own shortcomings rather than to 
h’s. At the same time I cannot but regard his style as 
considerably difficult and diffuse, and not perfect in the 
logical concentration which is so necessary for the clear 
enurciation of a theory. In some points his conclusions 
seem, undoubtedly, to agree with observations—for in- 
stance, as regards the vaporous masses that are formed 
over the spots, and which appear sufficiently attested by 
their strong absorption lines in the spectrum. In the 
main, however, I cannot say,so far as I may venture 
to give an opinion, that he has been more successful than 
other theorists on the same subject ; and among several 
objections which have occurred to me as affecting his 
views, I will venture to state the following :— 
1. Regarding the establishment of currents in the liquid 
envelope, Prof. Zéllner affirms that in this way alone 
could the more heated and specifically lighter portions of 
the liquid at the bottom make their way to the surface ; 
but this appears to me incorrect when we consider that in 
freezing water there is an interchange of the upper and 
lower strata until congelation begins, and this without the 
intervention of currents, 



2. He defines the spots as scoriaceous products floating 
on the liquid surface. The liquid, however, is moving in 
a current from the equator poleward, and, if so, I would 
ask how is it that the spots show no tendency to be carried 
along with it in that direction? I do not believe that 
any such general tendency has been observed. 
3. He makes no attempt to account for the very striking 
and suggestive appearances of the penumbra, which led 
Wilson to regard the spots as openings or depressions in 
the photosphere. Neither does he try to explain the dis- 
tinct boundaries of the nucleus, the umbra, the penumbra, 
the light bridges, nor the deeper shading of the penumbra 
round its exterior limits. 
4. The current cools in its advance poleward, and the 
polar regions are, as the professor tells us, the coolest 
parts of the sun. ‘Then if, according to his theory, the 
spots are the products of cold, why do they not increase 
in development up to the poles? He assumes, indeed, 
that the cold induced in the polar regions produces 
clouds in the atmosphere, which are unfavourable to the 
production of spots ; but they are so only as they check 
radiation and contribute to heat, and if, notwithstanding 
this, the polar regions are still found to be the coldest, 
and if cold is the cause of the spots, there seems a defect 
in the hypothesis. The professor points to an analogy 
between the spot zones and the clear zones of the trade 
winds oftheearth. The cases are, however, very different ; 
for our own atmosphere is subject to external influences, 
namely, the action of the sun, as well as those belonging 
to the earth itself. 
Of course,anything from the eminent pen of Prof. Zéllner 
must be received with the utmost respect, but I conceive 
that his theory of the sun-spots, as I have attempted partly 
to show, presents many difficulties ; and I cannot avoid 
stating my humble belief that, notwithstanding all that 
has been thought and written on the subject, and in spite 
of the modern discoveries of some of the constituent 
elements of the sun, we are but little nearer a true concep- 
tion of its organisation or economy than the theorists of 
the days of Hipparchus. 
J. BIRMINGHAM 


PROFESSOR TYNDALL ON THEORIES OF 
DISEASES 
WE reprint this article from the Sritish Medzcal 
Fournal, since it shows how closely connected are 
the most abstract inquiries with the most practical 
questions :— 
“The surest basis for Medicine is upon the broad 
foundations of exact scientific observation ; and we shall 
all welcome such contributions as so able a physicist as 
Professor Tyndall can make either to our knowledge or 
to our facilities for testing the foundations of our beliefs. 
The electric beam, which has in his hands played a large 
part in many able investigations and demonstrative ex- 
periments, was lately brought into play to demonstrate 
the ubiquity of dust in the atmosphere. To some very 
charming experiments Mr. Tyndall joined some theories 
which, if capable of proof, were yet not demonstrated by 
anything which he said or did. The ubiquity of these air- 
borne particles was perfectly well known, and their illu- 
mination by the electric beam, while it has given a more 
complete demonstration of their presence than was 
otherwise obtainable, has not added anything to our 
knowledge of their chemical or biological relations. His 
experiments, however, have had the valuable effect of 
demonstrating the uses of cotton-wool as a filter for them, 
and the advantage of inspiring him with interest in a 
subject in which we can but be pleased that one of ‘he 
most brilliant of investigators and expositors of physcal 
science should be interested — the investigation of the 
origin of zymotic disease, 
