JANUARY 24, 1907 | 
NATURE 
293 
to the theory in its existing state has pointed the way 
to its wide application in a great many cases. As the 
author repeatedly points out, the logical consequences 
of the electronic theory are still very far from being 
worked out in many of the subjects dealt with, and 
this task offers a fine field of investigation, which 
may ultimately lead to new results of the highest 
practical importance. 
Probably nowhere is this more true than in the’ 
field of electrochemistry, of which, however, the treat- 
ment is somewhat superficial and unsatisfying. 
Another topic, which fares even worse, and yet is one 
of which much might have been, and ultimately will 
be, made, is the optical activity of carbon compounds. 
What little is said is so misleading, for example the 
last sentence of chapter xii., that it should be either 
omitted altogether or considerably amplified. In the 
main, however, the treatment is refreshingly clear and 
interesting. 
Of course, it is to the explanation of that class of 
phenomena known as_ electromagnetic that the 
electron theory offers the greatest simplification. 
Consider a phenomenon such as *‘ the spark on break 
due to the extra E.M.F. of self-induction,’’ which is 
nothing but the electrical analogy of the water- 
hammer in a pipe when a cock is suddenly closed and 
the water stream stopped. For water read electrons, 
and for pipe read conductor, and even a beginner 
gets a clear mental picture of the phenomena. That 
all magnetic and electric phenomena are to be ex- 
plained by definite motions and properties of the in- 
dividual electron is a simplification that may be ex- 
pected to ameliorate the lot of the future student 
considerably. The electron theory provides for eiec- 
tricity that clear mental image of the processes 
involved, without which physical theories stagnate 
and become metaphysical. Nevertheless, the faculty 
of being able to think in more than one system is not 
easily acquired, and it is doubtful, for example in 
magnetism, if anyone trained on the present systems 
will ever really abandon them. 
In addition to the topics already alluded to, chapters 
are devoted to the electronic treatment of thermo- 
electricity, the Hall and allied effects, optical pheno- 
mena, the Zeeman effect, radiation, voltaic electricity, 
radio-activity, and the electric discharge. One chapter 
is devoted to a speculative effort, bold and imagin- 
ative, but logical, well considered, and unexception- 
able, on the similarity of the infinitely great pheno- 
mena of the cosmos with the infinitely small of the 
electronic universe. Finally, a new system of elec- 
trical quantities is advocated, in which electricity, 
represented by E, ranks as a fundamental quantity 
with length, mass, and time. The author uses 
throughout the expressions ‘‘ company of electrons,” 
“army of electrons,’’ to represent respectively the 
E.S. unit (2930 million) and the coulomb (8-79 
trillions), and thus once for all reduces electric quanti- 
ties to a definite number of electrons. 
Different readers will no doubt derive most benefit 
from different chapters according to their individual 
knowledge of the subjects referred to, but the book 
NO. 1943, VOL. 75| 
may be recommended to all interested’ in the progress 
of physical science. Dr. G. Johnstone Stoney, whose 
portrait appears as a frontispiece, contributes a pre- 
tace to the work. Beno: 
BOOK SHELF. 
By T. F. Cheese- 
OUR 
Manual of the New Zealand Flora. 
man. Pp. xxxvi+i1igg. Published under the 
authority of the New Zealand Government. (Wel- 
lington: J. Mackay, 1906.) 
TuE number of botanists who have contributed towards 
a knowledge of the New Zealand flora during the last 
forty years is remarkable, especially when it is recog- 
nised that their labours followed on discoveries made 
by earlier explorers and collectors of eminent repute. 
Banks and Solander, Colenso, Sinclair, and Hooker 
are a few of the early botanists whose work was 
collated in the ‘‘ Handbook of the New Zealand 
Flora,’’? compiled by Sir Joseph Hooker and published 
in 1864. Since that date, besides Colenso, Thomas 
Kirk stands out prominently as an energetic collector 
and author; he collected not only throughout both the 
main islands, but also visited several of the adjacent 
groups. Owing to his extensive acquaintance with 
the subject, in 1894 he was commissioned by the 
Government to prepare a flora of New Zealand, but 
the work was only half completed at the time of his 
death three years later. The task was subsequently 
entrusted in rgo01 to Mr. Cheeseman, who has contri- 
buted numerous papers on new species, on the floras of 
Three Kings and Kermadec Islands, and on special 
methods of fertilisation in various genera. The wis- 
dom of the choice is seen in the exhaustive and careful 
compilation now published. 
The arrangement follows the plan of Hooker’s 
earlier work, and to students of British botany ac- 
quainted with Bentham’s ‘British Flora’ this 
manual presents a familiar disposition. 
Turning to the subject-matter, as the result of the 
last forty years’ work, the computation of ferns and 
flowering plants has risen from about one thousand 
to nearly sixteen hundred species—exclusive of those 
naturalised—spread over 382 genera. With regard to 
orders the predominance of Composit is natural, but 
the flora is unusually rich in ferns and species of 
Scrophulariaceew, and poor in species of Leguminose. 
The number of species in some of the genera is very 
large, amounting to forty-three in Celmisia, of which 
all are endemic with one exception; Veronica shows 
eighty-four species, of which, in contrast to our con- 
ception of the genus, seventy-one form shrubs or small 
trees. The flora contains many curious plants and 
unique associations that have been graphically de- 
scribed by Dr. L. Cockayne, but from a systematic 
point of view the most extraordinary fact is found in 
the enormous proportion of endemic species, amount- 
ing to nearly three-quarters of the total. 
In working through a flora of such vast dimen- 
sions and containing so many exclusive species it 
will be comprehended that Mr. Cheeseman has 
accomplished a task of no small magnitude, and from 
the critical notes accompanying the technical diag- 
noses an idea is obtained of the wide knowledge and 
judicious discrimination that he has brought to bear 
upon it. The author and the New Zealand Govern- 
ment are both to be congratulated on the successful 
completion of the work. 
Evidence of incorporation of the latest discoveries is 
found in the new genus Townsonia and various new 
species. The author has provided in the appendices a 
