340 
NATURE 
[FEBRUARY II, 1904 
gravity, flash point, temperature of solidification, &c., 
of the most important of the oils now used for lubri- 
cating purposes, and a description of the apparatus 
commonly employed in connection with their deter- 
mination. 
Though the illustrations are, as a rule, clear enough, 
there are a few instances where it is difficult to follow 
the author’s description of pieces of apparatus owing 
to the fact that symbols used in the letter-press de- 
scription are not printed on the corresponding illus- 
tration. 
After a brief description of the various appliances 
used in connection with the distribution of the oil to 
the working parts of machines, the author discusses 
the comparative value of various lubricants from the 
point of view both of cost and of suitability for different 
classes of work. Ball-bearings and roller-bearings are 
dealt with in two chapters, but this part of the book 
is by no means so complete as the earlier portions; the 
last chapter, which explains ‘* forced ’’ lubrication, 
might with advantage be considerably extended in any 
new edition. The book, however, will be found very 
useful for reference purposes, both by those engaged 
in the design and by those who have charge of 
machinery on a large scale; information previously 
scattered through various publications has been 
brought together into a very compact form. 
The fact that Prof. Thurston’s book has now reached 
its seventh edition is a proof of how well it has done its 
work in spreading among engineers a knowledge of 
the importance of sound investigation into the energy 
losses brought about by friction and the best means of 
lessening them. The author, whose death we had so 
recently to deplore, has added much fresh matter in this 
new edition, and brought up to date the chapters deal- 
ing with experimental investigations on friction. In 
the additions Prof. Thurston describes the latest re- 
searches in regard to friction in high speed electric 
generators and motors, and in turbines; the experi- 
mental work of Lasche is summarised very fully and 
clearly, and his graphical methods of recording the 
results of various experiments by the three coordinate 
system are explained, the three coordinates being pres- 
sure, velocity and temperature of lubricant. The chap- 
ters dealing with lubricants and the best methods of 
testing them have also been considerably revised, and 
amongst other additions we notice several sections 
treating of roller and ball bearings. The book is now 
probably the best reference worl on friction at the dis- 
posal of engineers engaged in the design of machinery. 
at Jala 18}, 
THE FLORA OF THE SWISS ALPS. 
Geschichte und Herkunft der schweizerischen Alpen- 
flora. By M. C. Jerosch. Pp. vi+253. 
W. Engelmann, 1903.) Price 8s. ‘net. 
(Leipzig : 
HE attempt to trace the origin of a flora is so much 
a matter of speculative argument that it is only 
natural to find very divergent opinions expressed by 
different authorities. The object of this book is not to 
offer a new theory regarding the origin of the flora of 
NO. 1789, VOL. 69 | 
the Swiss Alps, but to bring together the views which 
have been put forward by leading botanists, partly for 
reference, partly with the object of comparing them 
and criticising them so far as it is possible to criticise 
the evidence of experts. 
The primary basis upon which to formulate hypo- 
theses is obtained by a comparison of the flora of the 
Swiss Alps with the floras of other regions in which 
many of the same plants are found. The occurrence 
of similar forms in the Arctic and Alpine regions is 
well known, and from the appearance of the species 
in different mountainous or Arctic regions it is possible 
to separate them into groups, such as the Arctic Alpine, 
the mid-European-Alpine group, and so on. The next 
step is to consider where these forms may have origin- 
ated. Take, for instance, a form which appears in 
the Arctic regions, in the Altai Mountains, and also in 
the Swiss Alps. Was the original progenitor a native 
oi any of these districts, or even elsewhere? By what 
path did it travel from one locality to another, and 
when? Some information may be gained by consult- 
ing geological records, and for this purpose the salient 
features of the post-Tertiary formations are submitted. 
A most important consideration is the effect of the 
Glacial period, whether the conditions were too severe 
or whether a portion of the present Alpine flora could 
have existed during the Glacial epoch; this has an 
important bearing on the age of the endemic species 
in the Alpine flora. On this, as on all hypothetical 
points, there is a great diversity of opinion. Christ, 
Heer, and Schroter are amongst those who favour a 
pre-Glaciai origin, but Schulz, Nathorst and Clement 
Reid hold the view that vegetation was very much re- 
duced at the best during the Glacial period. 
Then follows the most difficult because the most 
speculative question, which refers to the original home 
of these plants. To consider again those forms which 
have now found suitable conditions in such scattered 
| and diverse areas as the Arctic regions, the Alps, and 
the Altai Mountains, the Arctic region is postulated as 
the original source by Heer, Chodat and Pokorny; 
Hooker regards Scandinavia as the probable original 
home; Christ them back to the temperate 
regions of northern Asia, and considers that the Arctic 
regions merely represent the line of travel; and finally 
Briquet offers an entirely different solution, since he 
favours the possibility of the same species having 
originated in more than one locality. 
These examples will give some idea of the complex 
and difficult problems which confront the systematist 
who endeavours to unravel the past history of even a 
highly specialised flora, and will indicate how widely 
diverse are the explanations which are offered by well 
qualified investigators. It will be inferred that the 
writer has had no easy task in stating briefly and im- 
partially the various arguments. To weigh up definitely 
the pros and cons is impossible, but the criticisms of 
the author are very fair, and djsplay considerable 
acumen. The scope of the book is indicated by the 
fact that the bibliography covers ten pages, and not 
the least interesting chapters are those which discuss 
in of species and the climate of the Alps. 
refers 
