76 
condensed tables for alkaloids and gases, which are, 
however, in themselves very good ones. It is to be 
feared that these practical books tend to make students 
mere analytical machines in a small way, without giving 
them much real practical notion of chemistry. It is 
questionable whether a student who has worked through 
the modern tabular system of practical chemistry would 
be able, for instance, to state the reason for the employ- 
ment of bricks in preference to chalk for the back of an 
ordinary fireplace or some equally simple practical 
question, 
Elementary Chemical Arithmetic. By Sidney Lupton: 
(London: Macmillan and Co., 1882.) 
THIS little book with its modest preface will be recognised 
by all teachers of chemistry, especially in large laboratory 
classes, and also by students as a really useful adjunct. 
Unfortunately in large public laboratories a consider- 
able proportion of the studerfts have been very much 
neglected in the matter of their elementary mathematical 
education, or it has been of such a nature that they are 
not able to apply it to the solution of ordinary chemical 
problems, thus entailing, in many cases, a large amount 
of extra work and loss of time on the part of the teacher 
in giving instruction in elementary arithmetic. This 
book fits into its place exactly. It is divided into two 
main portions: an introduction, consisting of short but 
very understandable explanations of arithmetical pro- 
cesses in common demand in chemistry and physical 
chemistry of a practical and elementary nature, the 
second portion being problems divided under the headings 
of the different elements. Regarding these it may perhaps 
be said that they do not err on the side of being too 
chemical, and in one or two cases more attention has 
been given to the question as a question than to its abso- 
lute chemical correctness, but these are mere details that 
in no way detract from the utility of the book for its 
purpose. : 
What is required of the mass of chemical students is 
that they should be able to apply methods of reasoning 
founded on experimental facts in the science to the solution 
of concrete and abstract problems ; and working through 
this book will certainly conduce to bring about an 
improvement in that direction. 
The Watch and Clockmaker’s Handbook. By F. J. 
Britten. (London: Kent and Co., 1881.) 
THis little book has been written, we are informed, chiefly 
for the instruction of country watchmakers. It cannot 
fail to be agreeable to them: it contains a great deal of 
useful practical information, and some is given of a higher 
quality, such as workmen are, to their credit, eager for 
now-a-days. To another and wider circle there is also 
much of a character to be interesting. The book is a 
proper supplement to the more popular horological trea- 
tises. There are good descriptions and pleasing diagrams 
of the various watch escapements; there is a chapter 
upon the art of springing; the mechanism of chrono- 
graphs, repeating watches, and calendars is shown, but 
almost too briefly. Lastly, we find pictures and a short 
reference to the various tools which watchmakers employ, 
and some serviceable memoranda are added. Upon the 
whole the author has and deserves our praise. 
H. DENT GARDNER 
fTeroes of Science. Botanists, Zoologists, and Geologists. 
3y Prof. P. Martin Duncan, F.R.S.,F.L.S. (London: 
The Society for Promoting Christian Knowledge, 1882.) 
THIS little volume contains brief sketches of the lives of 
a few botanists, zoologists, and geologists, for the most 
part acknowledged compilations from well-known sources. 
No doubt the work will serve the purpose for which it is 
evidently intended—that of interesting young people in 
science. 
NATURE 
ies | 
| Mov. 23, 1882 
LETTERS TO THE EDITOR 
[The Editor does not hold himself responsible for opinions expressed 
by his correspondents. Netther can he undertake to return, 
or to 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 ts so great 
that it ts impossible otherwise to ensure the appearance even 
of communications containing interesting and novel facts.] 
Physics of the Earth’s Crust 
ON March 23 last Prof. Green sent to NATURE some remarks 
upon Mr. Hill’s review of my ‘‘ Physics of the Earth’s Crust.” 
More lately the third edition of his ‘‘ Physical Geology” has 
appeared, in which he has repeated the substance of a part of 
what he then wrote. On account of the great weight which his 
authority will carry, I think I should offer some reply. 
He truly says at p. 674, that I claim to have proved that the 
contraction of the earth through cooling cannot have caused the 
amount of squeezing and elevation which has taken place, and 
that the hypothesis is therefore insufficient to explain the facts 
which it professes to account for ; but he then adds: ‘‘ What 
Mr. Fisher has really done is this. His calculations go far to 
prove that, provided the earth cooled in the way assumed by Sir 
Wm. Thomson, contraction would not suffice to produce any- 
thing like the compression and elevation that has actually 
occurred, But this is quite another thing from disproving the 
contraction hypothesis. Mr. Fisher’s investigations tend rather 
to establish a strong probability that the earth did not cool in 
the way supposed by Sir Wm. Thomson,’—that is, that it be- 
came solid throughout in a comparatively short space of time. 
But of course my calculations do not establish any probability 
against this way of cooling, unless we begin by assuming that 
contraction through cooling has been the cause of the elevations. 
And that seems to be begging the question. What they do 
prove is that the contraction hypothesis will not account for the 
elevations if the earth has cooled as a solid. 
But there may have been another way of cooling which, on 
geological grounds, I believe to have beeen the true one. The 
earth may not have become solid throughout in a short space of 
time, and may not be solid even now. In that case the crust, 
whose corrugations we have to account for, must have floated on 
a denser liquid substratum. Under these circumstances every 
elevation above the mean level must have had a corresponding 
protuberance answering to it below. This is necessary, as was 
long ago pointed out by Sir G. B. Airy. I have, then, proved 
that, this being so, if the crust beneath the ocean is of the same 
density as beneath the continents, on what I conceive to be 
reasonable assumptions regarding the thickness and density of 
the crust and the density of the substratum, a shortening of the 
earth’s radius by less than 700 miles would not have sufficed to 
produce the existing inequalities. I can imagine no theory of 
the constitution of the interior that would admit of so large an 
amount of contraction taking place, after the whole had become 
sufficiently cool fora crust to have begun to be formed, as to 
cause such an amount of shortening as this. 
If, however, we suppose that the crust beneath the oceans is 
denser than that which forms the continents (and I have given 
several reasons for believing such to be the case), then a much 
smaller amount of radial shortening would suffice. I have esti- 
mated it at about forty-two miles. Still, anything near this 
shortening is far beyond what any reasonable amount of contrac- 
tion from cooling could produce. For if there bea liquid sub- 
stratum this must be of nearly equable temperature throughout, 
and that cannot be much above the temperature of solidification ; 
so that it does not appear how a much greater contraction can 
be got out of the gradual solidification, and incorporation of the 
upper parts of the liquid layer with the crust, than could be 
obtained on the former supposition of a cooling solid globe; and 
I have shown that, in that case, the ‘radial shortening would be 
less than two miles. 
- Thus, then, I claim to have disproved the contraction-hypo- 
thesis under the two alternative hypotheses (1) of a solid globe, 
and (2) of a liquid substratum, 
Capt. Dutton, of the United States Geological Survey, has 
said of this part of my work, ‘“‘ First and foremost he has 
rendered most effectual service in utterly destroying the hypo- 
thesis, which attributes the deformations of the strata and earth’s 
crust to interior contraction by secular cooling. No person, it 
seems to me, can sufficiently master the cardinal points of his 
