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NATORE 
| March 15, 1883 
oppose its spoliation, and everybody’s business is prover- 
bially nobody’s. It is to be hoped, however, that the 
kmell of these schemes was sounded on Monday last, 
when the House of Commons, on the motion of leading 
men of both parties, rejected the Chingford and High 
Beech Extension Bill, promoted by the Corporation and 
the Great Eastern Railway, by an overwhelming majority. 
The House was fully aware that the line then proposed 
by Sir Thomas Chambers and Lord Claud Hamilton was 
only the first section of a longer one which would ultimately 
surround the Forest, and that it was intended to serve at 
first mainly as a feeder to another large tavern. All 
lovers of nature will rejoice that the collecting ground of 
Edward Forster, the Doubledays, and thousands of 
London naturalists less known to fame, has been rescued 
from destruction. 
Authorities inform us that lopping and smoke have 
reduced the number of lichens and insects even during 
the last twenty years, and Conservatorial draining may 
have a similar effect upon other groups of organisms, so 
that the help of a railway in the work of devastation is 
certainly not required. 
It isto be hoped that the verdict of Parliament will 
show the Conservators that forest management has a 
scientific basis and that their powers are not unlimited. 
It is equally desirable that the public interested in the 
Forest will form some organisation for its protection from 
encroachment and mismanagement in the future, so as to 
relieve a scientific body such as the Essex Field Club, 
which has borne the chief labour of opposition, from a 
task which, from its political and litigious character, 
must necessarily be uncongenial. 
G. S. BOULGER 
PERRY’ S “PRACTICAL MECHANICS” 
Practical Mechanics. By John Perry, M.E. (London: 
Cassell, Petter, and Galpin, 1883.) 
HIS book is one of a series of manuals now being 
published by Messrs. Cassell and Co., intended for 
the use of technical students, and claims, to quote the 
preface, “to put before non-mathematical readers a 
method of studying mechanics,’ which, if carefully fol- 
lowed, will supply “a mental training of a kind not 
inferior to that the belief in which retains in our schools 
the study of ancient classics and Euclid.” A principal 
feature of the method consists in “ proving” the various 
formulz of mechanics by quantitative experiments. Of 
these many are described in the book, several of which, 
such as those relating to torsion and other stresses, &c., 
are carried on in many physical laboratories, and belong 
rather to physics than to mechanics. Another feature of 
the method more novel than the last is the gathering 
together of a few of the definitions and elementary 
theorems of mechanics, such as the parallelogram of 
forces, in a chapter at the end of the book called a 
glossary. Even then no formal proofs are given, probably 
because they are unnecessary, since on p. 2 we are told 
that the reader “ cannot know the parallelogram of forces 
till he has proved the truth of the law half a dozen times 
experimentally with his own hands.”’ 
This kind of proof is very different from the evidence 
usually tendered for the fundamental laws of mechanics, 
but we’must not forget the class of readers, entirely dif- 
ferent as they seem to be from any we have ever encoun- 
tered, for whom the book is intended. We are reminded 
of this on p. vii., when we are told that “the standpoint 
of an experienced workman in the nineteenth century is 
very different from that of an Alexandrian philosopher or 
of an English schoolboy, and many men who energetically 
begin the study of Euclid give it up after a year or two in 
disgust, because at the end they have only arrived at 
results which they knew experimentally long ago.” 
Thus the empire of the Greeks in geometry must give 
place to the supremacy of the intelligence of the working 
man, and even Euclid himself must fall from his high 
estate to be compared and contrasted with the modern 
schoolboy. But this latest born of time apparently pos- 
sesses even higher powers. If made “to work in wood 
and metal,” “to gain experience in the use of machines 
and use drawing instruments and scales,” he will arrive 
at a condition in which “he may regard the 47th proposi- 
tion of the First Book of Euclid as axiomatic,’ and “he 
may think the important propositions in the Sixth Book 
as easy to believe in as those in the First.” Truly here at 
last has been found in geometry a royal road. But when 
Prof. Perry has raised our opinion of the modern school- 
boy and working man to this high eminence we feel a 
rude shock on reading the second page of the book, when 
we discover that these rarely gifted, ideal beings, so 
favoured of the gods in geometry, may perhaps not be 
able to apply to a practical example a simple algebraical 
rule. 
In reading the book, especially in its earlier chapters, 
we are struck by the want of logical arrangement and of 
strictness in the definitions, by the frequent use of terms 
which have not been previously defined, or not adequately 
defined, and of writing so careless in its style as frequently 
to become unintelligible. The theory of friction, in the 
limited extent to which alone it is given, is inserted piece- 
meal into parts of the two first chapters and into the 
glossary, and the ordinary laws are not explicitly given 
until nearly the end of the book, but in their place we 
have the loose statements, “‘friction is proportional to 
load,’ and “friction is a passive force, which always 
helps the weaker to produce a balance.” The English of 
the last sentence is as curious in character as that of one 
on p. 13, “ This rubbing is a very slow motion.” 
The doctrine of the conservation of energy or of the 
conversion of energy into heat is nowhere explicitly given, 
although the theory is assumed in numerous applications. 
Can it be that the modern schoolboy, duly equipped, is 
able not only to surpass Pythagoras by regarding the 
47th proposition of Euclid as axiomatic, but that he has 
come to view the great physical theory as equally self- 
evident? It must be so; otherwise, having only been 
told of energy as the equivalent of mechanical work (p. 
5), he would not understand the meaning of the obscure 
sentence—* Every experiment we can make shows that 
energy is indestructible, and consequently, if I give 
energy to a machine, and find that none remains in it, it 
must all have been given out by the machine.” 
We find the leading laws of hydrostatics inserted in a 
paragraph on water, which is included in the chapter on 
materials, fifty pages after the uniform transmission of 
fluid pressure has been assumed in the article on the 
