August 6, 1885 | 
NATURE 
31 
on 
the writer had established his case in 1662. As to this 
there can hardly be two opinions ; and Prof. Tait is fully 
justified in insisting upon his objections to “ Mariotte’s 
law.” In Appendix IV. a curious passage from Newton 
is discussed, in which the illustrious author appears to 
speak of Mariotte sarcastically. It is proper that these 
matters should be put right ; but Prof. Tait is hardly im- 
partial enough himself to succeed in enlisting the com- 
plete sympathy of foreigners. Cases of glaring injustice 
should be rectified ; but there will always be a tendency 
(from which Englishmen cannot claim to be exempt) to 
give a full measure of credit to one’s own countrymen, if 
only because one is better informed concerning their 
labours. 
There is one matter, suitable to an elementary work, 
which I should be glad to see included in a future edition, 
viz., the principle of dynamical similarity, or the influence 
of scaze upon dynamical and physical phenomena. It often 
happens that simple reasoning founded upon this prin- 
ciple tells us nearly all that is to be learned from even a 
successful mathematical investigation ; and in the very 
numerous cases in which such an investigation is beyond 
our powers, the principle gives us information of the 
utmost importance. An example will make this clear, 
The pitch of a tuning-fork of homogeneous steel is de- 
pendent upon the size and shape as well as upon the 
elastic quality of the material; but the matter is too 
difficult for rigorous mathematical treatment. If, how- 
ever,'it be asked, How does the pitch depend upon the szze 
of the fork, the shape and material being given? we need 
no complicated mathematics at all. The principle of 
dynamical similarity tells us at once that the time of 
vibration is proportional to the linear dimension. 
Another example might be taken from a reaction which 
Prof. Tait describes as specially complex—viz., collision. 
A glass ball drops upon a marble floor from a height of 
one foot. How does the size of the ball affect the strains 
during collision and the danger of rupture? The prin- 
ciple teaches that if the scale of time be altered in the 
same proportion as the scale of length, similarity is 
secured, so that the strains are equal at corresponding 
times and at corresponding places. Hence a larger ball 
is not more likely to break than a smaller one, unless in 
consequence of thegreater duration ofthestrains. I feel 
sure that in Prof. Tait’s hands this very important and 
fundamental principle might be made intelligible to the 
great mass of physical students. 
It would lead us too far to refer in detail to the various 
subjects treated in the later chapters under capillarity, 
diffusion, ostnose, transpiration, viscosity, &c., but there 
is one point that I should like to mention. The explana- 
tion on p. 249 of the behaviour under water of drops of 
ink and of solution of permanganate of potash assumes 
the existence of a capillary tension in the surface separ- 
ating the two fluids. In my own experiments on jets 
with this very solution, 1 have never seen any tendency 
to break up into drops (as, according to Savart and 
Plateau, there would be in air), and have theretore 
supposed that the capillary force was wz/, or at any rate 
very small. Moreover, theory shows that the force 
depends entirely upon the suddenness of transition 
between two media, which suddenness must be broken 
down almost instantaneously when two miscible liquids 
come into contact. As the matter stands there seems to 
be here some discrepancy, which, perhaps, Prof. Tait 
could elucidate. 
In his preface the author holds out hopes of further 
volumes on the same plan, dealing with dynamics, sound, 
and electricity. The readers of the present work will, I 
am sure, join in the wish that the appearance of these 
may be delayed no longer than is absolutely necessary. 
RAYLEIGH 
GRISEBACH’S “VEGETATION OF THE 
EARTH” 
Die Vegetation der Erde nach threr klimatischen Anordn- 
ung. Ein Abriss der vergleichenden Geographie der 
Pflanzen, Von. A. Grisebach. Zweite vermehrte und 
berichtigte Auflage. 8vo. Vol. I., pp. 567; Vol. II., 
pp. 693. (Leipzig: Wilhelm Engelmann, 1884.) 
ROM the date, and the statement on the title-page 
that this is an augmented and corrected second 
edition of a work which was published in 1871, it might 
be expected that it contains the results of much mere 
recent investigation ; but an examination of the present 
edition is very disappointing. Indeed, it is douiful, to 
say the least, whether it deserves the descriptive title 
given to it ; for the “ Quellenschriften und Erlauterungen” 
do not appear to contain a single additional reference, and 
it is not easy to discover that it has a claim to be any- 
thing more than a reprint, with some trifling alterations, 
of the original edition of 1871. The author died in 1879, 
so that one naturally looked to see who was the editor of 
this edition, and it was only after much seeking that a 
clue was found in a foot-note on p. 15 of the preface, 
After the appearance of the “ Vegetation der Erde,” A. 
Grisebach continued to write annual reports on the pro- 
gress of geographical botany, and these, together with 
other scattered articles, were published in a collective 
form in 1880 by his eldest son, under the title, “ Gesam- 
melte Abhandlungen und kleinere Schriften zur PAlanzen- 
geographie.” From the foot-note in question it appears 
that this son—a gentleman in the Consular service of his 
country, and presumably unacquainted, or imperfectly 
acquainted with botanical literature—edited the new 
edition of the “ Vegetation der Erde,” “based upon the 
corrections and additions left by the author.” Now it is 
perfectly certain that Grisebach regarded the annual re- 
ports referred to as so many supplements to his greater 
work, and the substance of which he would doubtless 
have incorporated therein had he himself prepared a 
second edition. Since his death, too, considerable addi- 
tional information on geographical botany has come to 
light; and, what is more, it has been collected and 
published in German by Drude, Engler, and others ; yet, 
as already mentioned, the additions and corrections in 
the present edition are merely trivial, and cannot be said 
to enhance materially the value of the work. Ina foot- 
note to Grisebach’s preface to Tchihatcheff’s admirable 
French edition of the original work, reproduced here, it 
is stated that some additions of Grisebach’s thereto are 
here intercalated in their respective places. This is very 
good, but why Tchihatcheff’s copious annotations and 
additions, recognised and sanctioned, as it were, by the 
author himself, should be ignored in a second German 
