March 17, 1870] 
NATURE 
593 
sation. These concluding chapters stamp Mr. Galton 
as an ofiginal thinker, as well as a forcible and eloquent 
writer ; and his book will take rank as an important and 
valuable addition to the science of human nature. 
ALFRED R. WALLACE 
SPECTRUM ANALYSIS 
Die Spectral Analyse in threr Anwendung auf die Stoffé 
der Erde und die Natur der Himmelskérper. By Dr. 
H. Schellen, director der Realschule I.0., Cologne. 
(Brunswick, Westermann, 1870. London: Williams 
and Norgate.) 
HIS book contains an accurate and luminous account 
of the recent discoveries in celestial chemistry 
and physics, and especially of the researches of our 
countrymen Huggins and Lockyer. As regards the com- 
pleteness of that portion of the work bearing directly 
upon terrestrial chemistry, readers will, I fear, be dis- 
appointed. The first division of the book is devoted to 
a description of the means employed for the artificial 
evolution of light and heat of great intensity, beginning 
with combustions in oxygen, and ending with the 
electric-light. The second division is headed “The simple 
and compound spectra in their application to terrestrial 
matter;” whilst in the third and most important division 
Schellen considers the application of spectrum analysis to 
the heavenly bodies. The illustrations throughout the 
work are good, though many of them are not new, and 
are borrowed, without acknowledgment, from other 
books. 
With respect to the physical constitution of the sun, it 
behoves us in this, the infancy of our knowledge, to be 
very careful in drawing positive conclusions. In the first 
place, there is no doubt that whilst Kirchhoff’s original 
theory must undergo certain modifications, it will remain 
in its grand features as having first pointed out to us the 
true physical condition of the sun. The discovery of the 
chromosphere by Mr. Lockyer, in which, as a rule, only 
the bright hydrogen lines are seen, together with the 
yellow mysterious line of unknown origin, renders it 
difficult for us, especially if we accept Frankland and 
Lockyer’s conclusions respecting the excessive tenuity of 
the upper chromospheric layers, to suppose that an 
atmosphere containing iron and the other 13 difficultly 
volatilisable metals can exist outside the chromosphere of 
sufficient density to effect such a powerful selective absorp- 
tion as we see in the darkness of Fraunhofer’s lines. Hence 
we should be inclined to agree with Lockyer that the 
absorption does not take place, as Kirchhoff suggested, 
in a far outlying layer of solar atmosphere, or in what we 
term the corona, but that the dark lines are produced 
within the chromosphere. But, on the other hand, upon 
what known physical basis are we entitled to assume that 
the higher lying portions of the solar atmosphere consist 
almost entirely of glowing hydrogen gas, whilst the 
lower lying layers contain the more easily condensible 
gases of the other 14 elements? The well-known laws 
of gaseous diffusion (to say nothing of the cyclones of 
vast magnitude and of enormous rapidity, which Lockyer 
has taught us are constantly mingling up the various 
layers of solar atmosphere), forbid us to suppose 
that the lighter hydrogen gas can ascend whilst the 
heavier metallic gases remain quietly below. If the com- 
ponents of the solar atmosphere are gaseous, they must 
be uniformly, or nearly uniformly, mixed. How then can 
we account for the constant presence in the chromosphere 
of the hydrogen lines, whereas the lines of the other con- 
stituents of the solar atmosphere are scarcely visible, 
except in special cases of the occasional projection of the 
vapours of magnesium and other metals, whilst the ab- 
sorption is to occur in a lower gaseous layer, having 
a totally different composition ? 
Another point to be remembered is, that according to 
the law of exchanges the fact of the existence of ab- 
sorption 7ecesstfates the existence of a lower temperature 
in the absorptive medium than in the media (either 
above or below) in which such absorption is not ex- 
hibited, and which may either give continuous or 
broken spectra, according to the physical and chemical 
nature of the incandescent bodies. How then can 
the iron and magnesium vapour exist nearer to the 
white-hot body of the sun than the hydrogen and 
yet possess a lower temperature? I am here forcibly 
reminded of the plausibility of a suggestion thrown out 
by Kirchhoff, in a conversation with me a few weeks ago, 
viz.: that the upper regions of the solar atmosphere may 
be constantly illumed by discharges of electricity ; that 
the incandescent hydrogen may be heated not from below 
but from within its own mass, either by continuous flashes 
of lightning or constant auroral discharges ; and, indeed, 
Zollner has noticed the flashing out of certain bright 
points in the prominences, which may possibly be caused 
by solar lightning. 
We must also bear in mind that the existence in the sun 
of a solid or liquid white-hot nucleus, as originally assumed, 
is not proved by the results of subsequent research; inas- 
much as we learn from the recent researches of Frankland, 
Lockyer, and Wiillner (as indeed we may do from much 
older experiments), that incandescent gases under certain 
physical conditions emit white light and yield a continuous 
spectrum. So that spectrum analysis does not give us any 
certain information as to the physical state of that por- 
tion of the sun’s body from which the main portion of 
light and heat proceeds. H. E. Roscor 
OUR BOOK SHELF. 
Essays on Physiological Subjects. By Gilbert W. Child, 
M.A., F.L.S., F.C.S. Second edition, with Additions ; 
pp- 293. (London : Longmans, Green, and Co. 186c.) 
THE present edition of Dr. Child’s work is by no means 
a mere reprint of the last. It has undergone considerable 
modifications, chiefly in the form of additions, which will 
tend to make it more acceptable to a large class of readers. 
There is an almost entirely new essay on “ Some Aspects 
of the Theory of Evolution,’ in which he endeavours to 
show how this theory is related to religious belief. He 
believes its proper meaning and tendency to have been 
much misunderstood ; that far from being an “ atheistical” 
conception, it is in reality only the scientific form of 
natural religion. The subject of “ Physiological Experi- 
mentation on Animals” is also considered, whilst the last 
and longest essay, also new, is entitled “ Physiological 
Psychology,” in which he endeavours to make known to 
persons whose chief interest is in psychological rather than 
physiological science, all the chief points in the anatomy 
of the nervous system, necessary to be understood before 
he could explain, as he also attempts to do, the principal 
physiological conclusions which have been arrived at 
concerning brain action and mind. 
