98 
propulsion of balloons and on flight proper. It is 
illustrated by excellent photographs of both Zeppelin’s 
and Santos Dumont’s machines, and contains valuable 
statistical information in the form of tables, which will 
enable the reader to compare at a glance the means 
employed and the results achieved in attempts to 
navigate the air both by the Alus léger and the lus 
Jourd methods. A remarkable result shown by the 
tables is the very great advance. made in increasing the 
weight sustained per horse-power in the gliding experi- 
ments under gravity made by Lilienthal, Pilcher and 
Chanute, though the writer of the article expresses the 
opinion that the substitution of an artificial motor would 
reduce these results by one-half. Another table gives 
the resistance of surfaces at different incidences, cal- 
culated for planes by Duchemin’s formula and for 
curved wings from Lilienthal’s investigations ; and among 
other features we notice illustrated accounts of Chanute’s 
gliding machines, Langley’s and Hargreaves’ aérodromes, 
and Ader’s “ Avion.” With such information the reader 
will have little difficulty in forming a correct estimate of 
the present state of aérial navigation. 
It is difficult to summarise briefly the contents of 
the important article on “ A&ther.” The necessity for 
assuming the existence of an ether, the differences 
between ether and matter, the question as to whether 
the ther is in motion and the dynamical theories 
of the «ther form the chief themes of the article. At 
the present time “‘zther” has become an every-day word, 
but few who use it have much idea of what it means. 
The present article is clear and authoritative, and if it 
does not answer the unanswerable question, “‘ What is 
zther?” it does much to place this question on a sound 
and scientific basis. 
The article “Agriculture” deals, in two separate 
chapters, with the changes that the past quarter century 
has witnessed in British and American agriculture, and 
its most remarkable feature is the contrast which these 
two chapters present. The first begins with the observa- 
tion that the period 1875-1900 was a “fateful” one for 
the “greatest British industry,” and in the opening pages 
shows that floods and stock diseases characterised the 
first, and drought the last decade of this period ; that 
for every 100 acres under wheat in 1875 there were but 
fifty-four in 1900; that wheat worth 455. per quarter in 
the former year was worth 27s. in the latter, and that 
two Royal Commissions investigated the distressed con- 
dition of the British farmer. Passing from this melan- 
choly narrative to the chapter on agriculture in the 
States, we find the American writer revelling in the 
resources of his country. Between 1875 and 1897 the 
States farmer took possession of as much new land as 
would cover all France and Germany. 
_ “Since 1870 the production of nearly all farm crops 
increased more rapidly than the population, the most 
absolute proof of the prosperity of the people.” 
As a result of better implements and better tillage, the 
yield of wheat is gradually increasing, and will, it is 
believed, continue to increase. Much land is yet avail- 
able for wheat-growing, and the idea that a generation 
hence Americans will cease exporting wheat is regarded 
as quite erroneous. 
The illustrations of British live stock are excellent, and 
NO. 1700, VOL. 66] 
NATURE 
[May 29, 1902 
the specimens the photos of which are given prove that 
“depression” has not yet succeeded in wresting from 
our breeders the preeminent position they held when the 
ninth edition was published. We are proud of. our 
draught horses and we congratulate ourselves on their 
increase ; but so different is the American standpoint 
that the writer almost apologises for their presence. 
“Until the use of more and cheaper motors becomes 
possible, farm animals must increase with farming 
operations.” 
It is significant in this connection that all the illus- 
trations of animals are British and all the illustrations 
of machines American. Some of the implements shown 
are popular in this country, and some of them are largely 
manufactured here, but though the workmanship is 
British the ideas are exclusively American. 
Agricultural education and research are actively 
carried on in the States ; on research alone nearly 700 
workers are engaged. The English writer describes 
the work done at Rothamsted, ‘‘the greatest and the 
oldest of experiment stations” ; but Lawes and Gilbert 
are dead and there is no mention of progress. Are we 
standing still? The writer of the article “ Agricultural 
Machinery” prefaces his chapter by remarking that 
Americans, as implement makers, have gone “far ahead” 
of their rivals in the United Kingdom, and “ the following 
article is accordingly written from an American stand- 
point.” The volume does not inspire much hope, but 
hope and work we must if the next edition of the 
‘Encyclopedia Britannica” is to deal with agriculture 
from a Bridish point of view. 
Among the contributions on botanical subjects, the 
article on the “ Algze” is eminently satisfactory, not only 
as regards the array of facts, but also as incorporating 
the results of recent researches and the modifications in 
arrangement derived therefrom. The connection of the 
Cyanophycez with the Schizomycetes and the relation- 
ship of the Diatomacez to the Peridiniacez are pointed 
out. Evidence for and against alternation of genera- 
tions is fairly weighed up, while on polymorphism the 
conservative view of Klebs is maintained. The physio- 
logical principles underlying “Anatomy” are clearly 
brought out in dealing with non-vascular plants. But 
when the writer elaborates the stelar conception in con- 
nection with vascular plants these principles fall into the 
background. A tolerably safe course is steered through 
stelar difficulties, but no attempt is made to separate 
purely topographical changes from those of a morpho- 
logical nature. The ‘‘ Angiosperms” are treated almost 
entirely from the physiological point of view. Autotrophic 
plants are described as geophytes, aérophytes and hydro- 
phytes. The author’s views on phylogenetic relation- 
ships would have been extremely interesting, but dis- 
cretion overrules speculation. The systems of Bentham- 
Hooker and Engler-Prantl are merely outlined, while 
van Tieghem’s novel classification is shortly criticised. 
The article upon ‘‘ Universal Algebra” gives in three 
pages a summary account of the various special algebras 
which have been invented by modern analysts. Such, 
for instance, are Hamilton’s calculus of quaternions, 
Grassmann’s extensive calculus, and the barycentric 
calculus of Mébius. The article on “Algebraic Forms” 
