Marcu 18, 1915] 
NATURE 
61 

weeder left the field with a deep respect for his 
adversaries: so stubborn is the resistance that 
they offer, so various are the means by which 
they evade extermination. 
Here they all are, hundreds of them catalogued 
and described in this book, and although the 
weeds treated of are those which trouble the 
American cultivator, the English farmer and 
gardener will recognise many of his old foes. 
He will also learn not a little of new ways of 
fighting them. For America takes its weeds 
seriously—more seriously even than the good 
farmer of this country) He tracks them to their 
lairs in the hedgerows and keeps a sharp look- 
out on them in his neighbours’ plots. He even 
invokes legislation upon them. He needs be 
vigilant indeed, for field labour is not cheap or 
plentiful in his country, and the chief means of 
combating weeds—constant cultivation—cannot 
always be practised. We confess to a certain 
feeling of unmalicious pleasure, like that we have 
in the misfortunes of our friends, when we saw 
the weediness of the fields of certain parts of 
North America. Nevertheless, the American will 
win in his fight with weeds; for he threatens them 
with all the resources of organic chemistry. Not 
only are the sulphates of iron and of copper 
pressed into his service as weed-killers; but, and 
more recently, weeds are being attacked with fine 
sprays of kerosene or crude petroleum. 
The author of this manual writes with sureness 
on her subject. She knows weeds well, describes 
them admirably, and gives much sound advice on 
the methods to be adopted for their eradication. 
In fact, this is the best book yet published on 
weeds and one that will prove of considerable 
service to cultivators in this country. High 
praise must be given also to F. Schuyler Mathews 
for the excellence of the 385 illustrations. Their 
value is enhanced by the fact that they face the 
page of text on which they are severally described. 
One suggestion only would we offer in the 
interest of the busy reader of the book: that a 
new edition should include an appendix in which 
the means of control, and weeds controlled by 
these means, are classified. 

LANTERN- AND MICRO-PROJECTION. 
Optic Projection Principles, Installation and Use 
of the Magic Lantern, Projection Microscope, 
Reflecting Lantern, Moving Picture Machine. 
By Prof. S. H. Gage and Dr. H. P. Gage. 
Pp. ix+731. (Ithaca, N.Y.: Comstock Pub- 
lishing Co., 1914.) Price 3.00 dollars. 
lee use of the lantern in one of its many 
forms has become more and more general. 
In our younger days it was a great and excep- 
NO. 2368, VOL. 95] 

tional treat to see a magic lantern entertainment, 
but now there are kinematograph theatres in all 
Our main streets, and lanterns for the teaching 
of history, geography, and science in our schools, 
so that the younger generation look upon the 
lantern as a matter of course, and even the poorest 
of them go (perhaps too frequently) to the picture 
palaces. 
The number of operators using the lantern has 
thus enormously increased in the last few years, 
and the lantern is acquiring quite a literature of 
its own. The volume under review treats the 
subject very fully, and collects into one volume 
a large amount of valuable information on every 
aspect of the subject. It is intended to be avail- 
able to the ordinary unscientific rule-of-thumb 
operator, as well as to the manufacturer, and to 
the unscientific demonstrator or student. To 
meet the needs of the first of these, plain, practical 
directions are given in the earlier part of the book 
for using the direct-current arc, the alternating 
arc, the miniature arc, the lime-light, etc.; also 
practical summaries of what to do and what to 
avoid are added to each chapter, and there are 
similar practical instructions for using sunlight 
with a heliostat, for projecting opaque objects, 
for micro-projection, the kinematograph, and 
many other applications of the lantern. Pre- 
sumably with the idea of making each section 
complete in itself, there is a great deal of re- 
petition in these chapters. This will probably be 
of advantage to the practical man who is in- 
terested only in one form of projection, but it 
makes this part of the book tedious to read. 
In the later part of the book there are many 
valuable tables and curves giving, for instance, 
the relations between current, voltage, and candle- 
power of the different forms of arcs and _ their 
distribution of light intensity; also the light and 
the energy absorption of the various media— 
glass, water, etc.—that are used in projection 
apparatus; and the reflecting powers and light 
distribution of lantern screens. 
In the last chapter are some applications to 
physics. We should like to have seen this further 
developed; brief as it is, it explains how to 
demonstrate some beautiful experiments in ad- 
vanced optics—experiments which are not often 
shown. 
The instructions for adjusting the radiant are 
somewhat misleading. It is said that it should 
be placed at the principal focus of the first 
section of the condenser (§ 55), and it is said 
that there is a loss of light if the lamp is brought 
nearer. In almost every case this is not so, a 
bigger cone of light being embraced; in prac- 
tice the second lens of the condenser is not made 
