(f Z 
NovEMBER 22, 1906] NATURE 77 
door spiders, pocket-gophers, robber-crabs, squirrels, | sufficiently clear for their purpose. Part iv. of this 
ants, tree-frogs weaver birds, scarab beetles, and volume, on geographical surveying and mapping, has 
me hers eras in turn upon the stage. From the been practically re-written; the main heads dealt with 
SE ues aan I Sie are :—(a) the determination of fixed points, which in- 
nature of the case, a book that covers so wide a 
range must be in the main a compilation. But the 
authors add a good many observations of their own. 
Moreover—a very great merit this—-they investigate 
the current animal stories before accepting them as 
true. There is none of the credo quia mirabile spirit. 
They tell us, for instance, that the mole’s ‘‘ fortress ”’ 
is not the highly elaborated structure which a 
succession of books on natural history have each in 
turn still further beautified and complicated, but 
something much more varying and_ irregular. 
Altogether it is a very interesting book. The illus- 
trations, not very numerous, are good. 
(5) “Our School Out of Doors” is a book of a 
very different type. It contains a great deal of 
correct information on interesting subjects, but it is 
too misceilaneous, and it suffers from the plan on 
which it is arranged. Intended for the use of school 
teachers, it has one or more chapters for each month. 
This shifting from one subject to another, each very 
briefly and imperfectly explained, cannot be good for 
pupil or teacher. In May, Composite flowers are, 
apparently, to be studied before the pupil has any 
knowledge of the structure of a common buttercup. 
In August, five pages are devoted to ‘‘ watery 
wonders.’’ It would be far better to study some of 
the subjects more thoroughly and to neglect others 
altogether. 
OUR BOOK SHELF. 
Hints to Travellers, Scientific and General. Edited 
for the Council of the Royal Geographical Society 
by E. A. Reeves. Ninth edition, revised and 
enlarged. Two vols. Vol. i., pp. xi+470; vol. ii., 
pp- v+286. (London: Royal Geographical Society, 
1906.) Price 15s. net. 
IN editing this ninth edition of the well-known 
“Hints,’’ Mr. Reeves has taken a point of view some- 
what different from that of his predecessor, Mr. John 
Coles, in the earlier editions. He says :—‘‘ As the 
days of the pioneer explorer of the old type are fast 
drawing to a close . . . more exact surveys are re- 
quired than were formerly considered sufficiently 
accurate for the traveller in unexplored regions.’’ 
Hence, in the first and larger volume, which is, as 
before, wholly devoted to surveying and mapping, 
some of the approximate methods, and the tables con- 
nected with them, have been omitted, and a higher 
standard of accuracy is aimed at throughout. While 
it seems possible that the effect may be to discourage 
some travellers who could still do quite useful survey- 
ing work from attempting anything at all, and in 
others to transform a journey in an unexplored region 
into a surveying expedition pure and simple, it re- 
mains unquestionable that Mr. Reeves has produced. 
a condensed treatise on surveying of a high order of 
excellence. x 
In the section on instruments, the chief new 
features are the descriptions of the applications of 
Mr. Reeves’s devices, the ‘‘ tangent-micrometer *’ and 
“endless tangent screw,’ to the theodolite and 
sextant. It may be noted that the illustrations of the 
transit theodolite on pp. 29 and 40 are distinctly in- 
ferior to those in the older editions, and are scarcely 
NO. 1934, VOL. 75] 
cludes triangulation with the transit theodolite, lati- 
tude and azimuth traverses with normals of angles 
from stations on the route, and latitudes and longi- 
tudes; (b) the filling in of detail and route surveying ; 
and (c) the determination of heights. The first of 
these sections contains much new and useful matter 
relating to interpolation, reduction to centre, and 
geodetic computations. The fifth division, on astro- 
nomical observations, has also been to a great extent 
re-written; the methods of determining longitude by 
means of lunars, moon-culminating stars, and the 
eclipses of Jupiter’s satellites are omitted, and the 
space devoted to more complete descriptions of the 
observations for latitude, time, and azimuth, great 
additional clearness being gained in the computations 
by the free use of diagrams and formula. The only 
absolute method of determining longitude described 
is that of occultations. 
In the second volume the chief new feature is am 
extremely valuable section on archeology, by Mr. 
D. G. Hogarth, which gives general hints on methods 
of recording, cleaning, temporarily conserving, and 
conveying monuments and objects of antiquity. 
Sechs Vortrége iibey das thermodynamische Poten- 
tial, Gxc. By J. J. van Waar. ‘Pp. viiit 119. 
(Brunswick: Vieweg und Sohn, 1906.) Price 
3.50 marks. 
Tuis pamphlet of close upon 120 pages really con- 
tains eight lectures, the first and second being, as 
stated in the expanded title, on non-dilute solutions 
and osmotic pressure respectively. These two intro- 
ductory lectures are polemical, and attack in a lively 
manner the position assumed explicitly by some, 
implicitly by many, that the so-called osmotic pressure 
is a real pressure due to the molecules of the solute. 
The author pokes fun at the ‘dilute school’ for 
pinning their faith to the first term of a diverging 
series, and for leaving out of account in all their 
theorising that most essential thing in osmosis, the 
semi-permeable membrane. He shows that instead 
of the ‘‘ osmotic pressure ’’ depending on the solute, 
it depends fundamentally on the solvent, being mathe- 
matically expressible to a first approximation in terms 
of the difference of the molecular potentials of the 
two solutions separated by the membrane. He makes 
an appeal in favour of the use of the thermodynamic 
potential, which is applicable to all cases, including 
those of weak solutions, for which alone the method 
of the osmotic pressure is of any real service. 
According to his facetious comparison, to explain the 
accompanying phenomena by an appeal to osmotic 
pressure is as if one explained an angry man’s hasty 
speech as due to his red face. The anger is the 
cause of both; and in like manner the thermodynamic 
potential forms the basis of the true theory. Then 
follow the six lectures on the thermodynamic poten- 
tial and its applications to the problems of chemical 
equilibrium. 
Lecture i. begins with entropy, deduces the usual 
thermodynamic relations, and finishes with the 
general conditions for equilibrium. The next lecture 
contains some simple illustrations leading to the re- 
cognition of particular cases of Gibbs’s phase rule. 
This important rule is proved in lecture iii., and 
more complex cases are considered of mixtures of 
solids, liquids, and vapours. The fourth lecture dis- 
cusses the thermodynamic properties of mixtures of 
ideal gases, deduces Gibbs’s dissociation formula, and 
applies it to certain simple cases. The effects of 
