Fuly 14, 1870} 
NATURE 
209 
illustrations, the strains of lively music which we are 
told accompany every movement, and, above all, the 
repeated assurance that the ladies need do no more than 
they like, will all tend to persuade parents and daughters 
that gymnastics are very pleasant and desirable. 
On Eozoin Canadense. By Professors King and Rowney. 
8vo. (Dublin, 1870.) 
THIS reprint from the Proceedings of the Royal Irish 
Academy, treats of a controverted subject of considerable 
interest to geologists and zoologists, namely, the nature 
of certain Canadian and other serpentinous limestones in 
which Logan, Dawson, Sterry Hunt, Carpenter, Jones, 
Giimbel, and others believe they find definite traces of a 
foraminifer known as Zosodu. Great difference of 
opinion on the subject under notice has been expressed 
during discussions before learned societies and in memoirs 
written by geologists, some seeing under the microscope 
good proofs of the presence of foraminiferal structure ; 
and these observers are mainly rhizopodists well ac- 
quainted with the peculiar structures of shelled protozoa, 
others finding nothing but inorganic fibres, globules, 
floceuli, &c., of mineral matter in both the Canadian and 
any other similar serpentinous marbles. Among the 
latter disputants are Doctors King and Rowney ; and in 
the paper before us there are some new descriptions and 
figures of specimens illustrative of the structure of certain 
ophitic rocks from different countries, and likely to be 
of use to “eozodnal” students, enlarging their field 
of observation, and aiding them, perhaps, in arriving at 
definite conclusions. The figures, however, are little 
better than diagrams, and cannot help the student much. 
The paper is largely composed of criticisms on the 
researches and remarks of others, in a highly disputatious 
form, and not enriched with anything new to those who 
have thoroughly studied the matter, either mineralogically 
or from a zoological point of view. The following im- 
portant facts do not appear to be recognised by the 
authors : first, that ophites, on the one hand, may not be 
really “eozoénal” and yet have mineral structure re- 
sembling in one point or another what occurs in Eozoon , 
secondly, that true eozoénalrockis often so greatly crumpled 
up in its metamorphic state, that patches only of the | 
organic structure are found here and there amongst the 
somewhat similar ophitic mass of granules and fibres, 
Die Ophthalmologische Physik, und thre Anwendung 
auf die Praxis. Von Dr. Hugo Gerold, of Giessen. 
Part 1. (Vienna, 1870. London: Williams and Norgate.) 
THE advances in the department of Ophthalmology have 
of late years been so rapid and important, that either 
thoroughly-revised editions of the standard works or alto- 
gether new books have become a sheer necessity. The 
volume before us comes under the latter category, and is 
the work of a gentleman well known as an able physicist. 
The present part is occupied with the Dioptrics of the 
Eye; the defects in it that are due to spherical and 
chromatic aberration; the terminology employed to 
indicate the different functional relations of the several 
parts to one another and to light, as zequatorial, median, 
and sagittal planes, axes, visual lines, field of vision, angle 
of elevation, &c.; the principles of perspective and 
of the construction of the microscope, the ophthal- 
moscopic investigation of the eye, and the adaptation of 
convex and concave lenses for hypermetropia or myopia, | 
and lastly, a section on light and colour. The parts we 
have read appear to be clearly and intelligibly given, and 
with something like French method and order. The 
mathematical formulze introduced are not beyond the 
comprehension of an ordinary well-instructed reader, and 
the diagrams are numerous (123 in number) and instructive. 
EG 
LETTERS TO THE EDITOR 
( The Editor does not hold himself responsible for opinions exprzsssd 
by his Correspondents. No notice is taken of anonymous 
communications. | 
Prof. Pritchard and Mr. Proctor 
It has been pointed out to me that Prof. Pritchard, engaged 
as he isin many important avocations, may quite unwittingly 
have misjudged my treatise onthe Plurality of Worlds. Treadily 
(eagerly) admit this, and also that, in this case, I owe the es- 
teemed Savilian professor an apology for suggesting that he has 
intentionally wronged me, 
The matter is now reduced to a simple issue. I have sub- 
mitted considerations which are sufficient to convince Prof. 
Pritchard that his critique is not just. If he withdraws his un- 
favourable comments, as resulting from accidental miscon- 
ception, I shall be bound to apologise for too hastily charging 
him with deliberate unfairness. If he will not, I cannot truth- 
fully withdraw my objections. I will not endure to be repre- 
sented as speaking severely (and by inference unfairly) of men 
for whom I have (and have expressed) a most sincere and un- 
qualified admiration—of such men, to wit, as the Herschels, 
Tyndall, Lassell, Balfour Stewart, and Sir W. Thomson. 
RICHARD A, PRocToR 
Whence Come Meteorites? 
I HAVE read, with great interest, in the number of June 2nd of 
your journal the article which Mr. N. S. Maskelyne has devoted to 
the examination of my theory on the Origin of Meteorites. I 
request permission to offer some observations on the criticisms of 
that learned mineralogist. 
Although Mr. Maskelyne concludes by saying that, in his 
opinion, I have not attained the end which I had proposed to 
myself, I will attempt to show that my system has, in fact, per- 
fectly resisted his attacks. 
In truth, the views I have been led to take on the subject of 
meteorites are not by any means simple fruit of my imagination. 
I have been led to them by the observations of material facts easy 
of verification ; and it is only in the background, so to speak, that 
| I have brought under consideration different consequences, which 
may certainly be matter for discussion. Now, in Mr. Maskelyne’s 
argument, he has given the place of honour to these secondary 
considerations, whilst he has left the real substance of the question 
completely in the shade. A few lines will suffice to justify my 
assertion. 
The chemical and mineralogical study of the specimens which 
compose the rich collections of meteorites at the Museum of 
| the Jardin des Plantes has made me acquainted with polygenic 
masses—that is to say, masses formed of angular fragments 
soldered together, but possessing each one such decidedly sepa- 
| rate characters that it is impossible to suppose that they were ori- 
ginally produced in the forms and in the relative positions which 
they present at the present day. These clastic meteorites had 
| been previously studied ; but not, as far as I am aware, from the 
point of view at which I have placed myself. 
From the studies and experiments I have made on this subject 
results the indubitable fact that the fragments, the union of 
which constitutes various clastic meteorites are, each one, com- 
pletely identical with well-known monogenic meteorites. It is 
thus, that the clastic meteorite of St. Mesmin (May 30, 1866) 
contains angular fragments rigorously the same in every respect 
as those which would be produced by breaking up the meteorite of 
Lucé (Sept. 30, 1768) ; fragments soldered together by a dark 
coloured cement exactly similar to the substance which forms the 
principal mass of the stone of Limerick (Sept. 30, 1813). It is 
thus also that in the same cement, the meteorite of Canellas (May 
14, 1861), contains fragments of a rock impossible to dis- 
tinguish from that of which the mass of Montrejeau (Dec. 9, 
1858) is a specimen. 
How is it possible to understand these positive facts without 
having recourse to the explanation, so evidently true of terrestrial 
fragments? For fragments of two distinct rocks to be found as- 
| sociated in one clastic mass, it is absolutely necessary that these 
two rocks should come from a region where they were in con- 
nection. Thus, on one hand, the rocks of Lucé and of Limerick 
were in connection; thus, on the other hand, the rocks of 
Montrejeau and Limerick were in connection ; then, in conclu- 
| sion, the rocks of Lucé and of Montrejeau were in connection. 
