Sept. 3. 1885] 
NATURE 
413 
Un Capitolo di Psicofisiologia. Da Enrico dal Pozzo. 
Foligno, 1885.) 
A GooD book on abnormal mental phenomena of all sorts 
was to be expected from Prof. dal Pozzo, one of the very 
oldest living investigators of this branch of physiology in 
Europe. The present excellent little treatise comprises 
the substance of seven lectures delivered during the 
current year to the medical students at the University of 
Perugia on “ Hypnotism,” “ Animal Magnetism,” “ Som- 
nambulism,” “Human Radiation,” and “ Psychism.” 
The whole field is thus covered from the time of 
Mesmer down to Mr. Crookes’s experiments, and the 
still more recent ‘“‘ Thought Readings” of Mr. Bishop 
and Mr. Cumberland. As a philosopher of the monist 
school, the author naturally rejects the spiritualistic con- 
ception, accepts the term “psychism” only in Mr. 
Crookes’s sense, and regards all these manifestations as 
strictly co-related and explicable on physiological grounds. 
Human radiation he is also disposed to admit as a bio- 
logical property, hence has no difficulty in believing in 
such well-attested facts as may be explained by it. But 
whatever cannot be so explained he regards as unworthy 
of credence, and treats the terms “ spiritual,” “ transcen- 
dental,” and the like, as synonymous with ignorance. 
The power claimed by paid mediums to hold commune 
with the departed is, of course, emphatically denied, and 
it is cogently argued that the medium can tell us nothing 
regarding present or past facts of which the audience may 
be ignorant. He cannot, for instance, say how many 
chairs are in the next room if the number is unknown to 
all present, whereas the somnambulist will often tell it 
exactly. Hence if these psychic manifestations did not 
depend on human radiation, but were the work of spirits, 
it would follow that these spirits are more ignorant than 
ordinary somnambulists. And to the assertion that 
psychism produces phenomena absolutely inexplicable by 
human radiation, the answer is that who cannot do the 
less can scarcely do the more in matters of this sort. 
At the end of the work a chapter is added on Giordano 
Bruno, and his philosophic system, which, although not 
directly connected with the subject, will repay perusal. 
Die Nutzbaren Pflanzen und Tiere Amerikas und den 
alten Welt vergleichen in Bezug auf thren Kulturein- 
Jiuss. Dr. L. Hock. (Leipzig: E. Engelmann, 1884.) 
IN a pamphlet of fifty-eight pages Dr. Hock institutes a 
comparison between the useful plants and animals em- 
ployed by man in the two hemispheres. Although the 
comparison is made in a somewhat rambling manner in 
the text, the conclusions arrived at are clearly tabulated in 
the form of anappendix. The influence of useful plants and 
animals on civilisation seems almost lost sight of, except 
on p. 10, where guesses at their mode of influence, rather 
than evidence proving it, are offered. Only those species 
considered by Dr. Héck to be the most important to 
mankind are noticed ; hence the comparison can only be 
regarded as approximate to the truth. The author finds 
that the Old World or eastern hemisphere affords 269 
useful plants and 58 animals against 52 plants and 13 
animals derived from the New World. In consideration, 
however, of the larger area of the eastern than of the 
western hemisphere, which he estimates as being in the 
proportion of 9 to 4, he concludes that the New World 
only affords rather more than half so many as the Old. 
The tables in the appendix indicate a certain amount 
of carelessness or confusion, which slightly vitiates 
the conclusions arrived at. Thus, Cz¢rullus Colocynthis 
and Momordica Elaterium are classed under fruits used 
as food, instead of under medicinal plants; Aumex 
Patentia is indicated as English spinach, and H/aema- 
toxylum campechianum, which is stated in the text to be 
a New World plant, is given in the appendix as belong- 
ing to the Old World. It is difficult to understand the 
principle upon which the “more important” plants have 
been selected, many of them being by no means so ex- 
tensively used as others which are omitted ; this is par- 
ticularly noticeable in the list of medicinal plants and 
those used in the arts. But, in justice to the author, it 
must be admitted that the task he has undertaken is a 
most difficult one, and cannot be fully treated in so small 
a space as he has given to it. Hisclaims that the greater 
proportion of the present work was already completed 
before De Candolle’s “ Origin of Cultivated Plants” fell 
into his hands must also be allowed due weight. 
LE TRERS GO TLE EDITOR: 
[The Editor does not hold himself responsible for opinions expressed 
by his correspondents. Neither can he undertake to return, 
or lo correspond with the writers of, rejected manuscripts. 
No notice is taken of anonymous communications. 
[The Editor urgently requests correspondents to keep their letters 
as short as possible. The pressure on his space is so great 
that it is impossible otherwise to insure the appearance even 
of communications containing interesting and novel facts.] 
Iona 
BEFORE the close of the season when there is easy, and indeed 
luxurious, access to the Island of Iona by steamers from Oban, I 
would call attention to the high interest which attaches to its 
geology in connection with the rocks now called ‘‘ Archzean.” 
Although the rocks of Iona are lithologically very distinct 
from the old gneiss of the Hebrides (which is the true ‘‘ Lauren- 
tian” and closely resembles the rocks near Quebec), yet they 
are equally distinct from the mica slate series of Argyllshire, and 
I have always regarded them as undoubtedly belonging to the 
pre-Cambrian horizons. I had never seen, however, until last 
week, the beautiful sections exhibited in the precipices of the 
south-west corner of the island. Tourists often visit the little 
“Bay of the Coracle,” where St. Columba is said to have landed, 
and I had not myself gone farther west. But the very calm sea 
of last week tempted me to boat round the farther coast to the 
south-west, and I was much struck by the sections there seen. 
The 1ocks are quite free from vegetation, and the exhibition of 
the strata is very striking. They are intensely hard and highly 
silicious—beautifully coloured with red, green, and black—and 
the beds dip at a high angle with remarkable flexures and faults 
of all kinds. 
On the side of the island where the cathedral is, and which 
tourists visit, the rock is entirely different in its mineral aspect 
and character—being a dark or black slaty rock, thinly bedded, 
and with no bright colouring at all. It belongs, however, evidently 
to the same series, and has generally the same dip and strike as 
the beds farther west. 
I should be very glad if some geologist acquainted with the 
different horizons of the Archzean series so largely developed in 
Canada could visit Iona, and determine to which of these horizons 
its rocks belong. Between them and the mica slates of the 
mainland of Argyllshire there is interposed the massive granite 
of the Ross of Mull—which comes up close to the eastern shore 
of Iona, avd on the other side of which, near Bornepan, the 
mica schists are in the same relative position ; while underneath 
the granite itself, and sometimes interbedded with it, there are 
some beds of a dark hornblendic gneiss. 
The whole neighbourhood is evidently one of great interest in 
connection with the oldest metamorphic rocks of our island. 
s.s. Columba, Campbelltown, August 30 ARGYLL 
Radiant Light and Heat 
THERE are two points in my article of last week which I 
should like to have the opportunity of discussing at somewhat 
greater length. 
(1) In this article I made use of the following expression, 
having especial reference to phosphorescent bodies which con- 
tinue after excitement to emit luminous rays at a comparatively 
low temperature :—‘‘ There seems to be no reason why molecular 
energy should not be somehow changed at once into radiant light 
and heat.” Let me now explain what I meant by this state- 
ment. The concluding quotation from Prof. Tait leads us to 
see that the definite connexion between the quantity and quality 
of the heat and light given out by a body and the temperature 
of that body, which the theory of exchanges asserts, is only 
statistically true. I can imagine, therefore, a few neighbourin g 
