166 
NATURE 
[Fune 24, 1886 
tion is deduced and its consequences investigated, 
especially in helping to find potential. Spherical Har- 
monics occupy the next thirty-two pages. The very con- 
venient and appropriate name “Laplacian” is here 
assigned to the important “ Laplace’s coefficients”: by 
analogy the name “ Legendrian” might well be applied 
to Legendre’s coefficients ; short terms of this kind are 
useful, and commemorate the inventors. The usual de- 
velopments are given; the applications to symmetric 
bodies are interesting, e.g. a potential function (ze. one 
such that V2v = 0), which is the potential of a sym- 
metric body for all points on its axis, is ¢#e potential of 
the body. 
Chapter XVIII. (103 pp.), on Small Strains and 
Stresses, is divided into three sections. 
Sec. I. (32 pp.). Small Strains.—This treats of the sza// 
strains (changes of shape or size) of a body without refer- 
ence to their causes. It is shown that straight lines, 
planes, and parallels remain such, whilst spheres become 
ellipsoids, &c., and there is always one line of no rotation 
at every point. It is also shown that every strain may be 
resolved into a pure strain and a rotation, and that the 
strain proper may be produced by three elongations, or 
by one elongation and a contraction all round an axis 
(this is called traction). Torsion is shown to be equiva- 
lent to shear, and shear to be equivalent to an extension 
and contraction, &c. 
Sec. II. (22 pp.). Stress.—This treats of internal stress | 
apart from concomitant strain. The usual composition 
and resolution are investigated, the work of an actual | 
strain and the virtual work of virtual strain are found, 
and the latter is shown to be an exact differential. 
Sec. III. (49 pp.). Stress and Strain.—The relations 
between the moduli of compression (4) and distortion (i), 
the contraction-coefficient (7), and Young’s modulus (/) 
are first traced for isotropic bodies, and the strain- and 
stress-potentials found for the same, and it is shown that | 
every force-system produces definite strain. The work 
in pure compression and pure twisting is investigated, 
and it is shown that twisting couples applied at ends of a 
cylinder produce pure torsion only in a circular cylinder, 
so that in other cases the plane sections are deformed. 
The theory of the slightly bent plane beam is investi- 
gated as far as the theorem of three moments. In hetero- 
tropic bodies it is shown the conservation of energy 
reduces the number of independent elasticity- coefficients 
from thirty-six to twenty-one. St.-Venant’s reduction to 
fifteen for cases where the mutual action of two particles 
is independent of other particles is discussed, and is 
shown to lead to the value n = ; for the lateral contrac- 
tion-coefficient of an isotropic body. Maxwell’s researches 
on the propagation of gravitation are reproduced, and 
are described as showing that gravitation could be pro- 
duced by a certain stress over a closed surface propa- 
gated through an all-pervading medium (ether) transfer- 
ring strain like a solid, but further research shows that 
this ether is not quasi-solid. 
Chapter XIX. (45 pp.). Electrostatics.—After the usual 
elementary propositions it is shown that a “line of force” 
meeting an electrified conductor obliquely is refracted, 
and that the charge-distribution over an isolated body is 
determinate : this leads to interesting problems in soap- 
bubbles. It is shown from Green’s equation that a 
hollow conductor screens its contents from outer electric 
disturbance ; thishas a practical application in protection 
of delicate instruments inside a metallic cage. Lastly, — 
the theory of electric images is discussed, and examples 
given. j 
From the full analysis given it will be seen that the 
work is a most important one: it is, in fact, one of the 
best treatises of the day. 
ALLAN CUNNINGHAM, Major, R.E. 
we, 
THE CRUISE OF THE “BACCHANTE” 
The Cruise of Her Majesty's Ship “ Bacchante,’ 1879-82. 
Compiled from the Private Journals, Letters, and Note- 
books of Prince Albert Victor and Prince George of 
Wales, with Additions by John N. Dalton. Two Vols. 
(London : Macmillan and Co., 1886.) 
O us the chief interest of these two bulky volumes 
lies in the fact that they are the record of what we 
may call the technical education of our future King and 
his brother. It was a right and proper thing for the 
Prince of Wales to do to see that his sons should become 
personally acquainted with the leading sections of that 
great Empire with the conduct of which they will in the 
future have so much to do. Indeed, in these times, when 
our colonies are coming so conspicuously to the front, 
when their affairs are regarded as of Imperial importance, 
it might be a good thing to insist that our Colonial Secre- 
taries should follow the princes’ example, and that no one 
should be considered qualified for the post of Minister for 
the Colonies who had not studied their affairs on the spot. 
Technical education is considered essential nowadays to 
any one occupying a responsible position in even the 
humblest of callings; but we fear that statesmanship is 
still beyond the pale of science. 
In the volumes before us Canon Dalton has the lion’s 
share. The princes’ contributions have been edited by 
him from their diaries, note-books, and letters ; while he 
himself contributes long sections in which he brings to- 
gether much useful information, and discussions on the 
affairs of the various colonies visited. Of course the 
writings attributed to the princes are no doubt much 
indebted to the superintendence of their tutor; at the 
same time the boyish hands can be traced throughout. 
The whole work is creditable both to the princes and to 
Canon Dalton. They certainly worked hard both at their 
books and at their duties as middies ; for in all respects 
when on board ship they were treated precisely as their 
mates. They evidently took a genuine interest in their | 
duties on board ; took a pride in mastering all the details 
of navigation and the working of a war-ship like the 
Bacchante,; were as eager to pass their examinations as 
if their future careers depended on the result. Much of 
their share of the work consists of details as to the day’s 
cruise, their own work as officers, the exercises proper to 
such a ship, and the incidents of the gun-room. Mixed 
up with this are the results of their own observations in 
the countries visited, information gathered during their 
visits or from books, their experiences when sojourning 
in the colonies, in Japan and other countries, with occa- 
sional reflections suggested by all this. Canon Dalton’ 
contributions are more solid and serious. He enters int 
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