24 
NATURE 
[Vov. 10, 1870 


catch, and it is very hard to get him to see how to 
express it in any but the simplest case. On the other 
hand, we have no clear notion of Force at all until we 
master it, and statics without that idea is a series of 
barren propositions, which stand to real life much in the 
same relation as a “uniform, weightless, perfectly rigid, | 
straicht rod” does toa real bar. M. Fernet accordingly 
places this conception at the commencement of his book, 
and we find the laws of uniformly accelerated motion 
given before the discussion of levers and centres of 
gravity. 
It is extremely easy, and perhaps a little ungracious, to 
select for notice points the omission of which causes 
surprise even in an elementary work of 800 pages. 
need of compression, which constrains an author who has 
to treat in one volume mechanics, hydrostatics, pneu- 
matics, light, heat, sound, electricity, magnetism, and 
meteorology, is so great, that it is impossible to question 
too loudly the prudence of obvious omissions. But we 
should have expected to find a little discussion of the | 
adhesion of liquid plates to the solids which they wet, 
and to each other, ; and one would willingly excuse the 
absence of the regulation picture of the balloon and its 
car, with the accompanying history of the brothers Mont- 
golfier, for an account of the mercurial air-pump of 
Sprengel or Jolly. M. Fernet is perhaps a little open to 
the charge which is constantly brought against the scien- 
tific men of his country, that if they read anything but | 
the science of the Comptes Rendus and the Aznales 
de Chimie et de Physique, they never indicate the fact by 
a line or an allusion. M. Verdet alone, of well-known 
French scientific writers of our time, knew German and | 
English as well as French science, and showed that he 
knew it. We should scarcely have found any book of 
his on the subject of heat, without any reference—as 
far, at least, as I can find—to Joule’s principle of the 
equivalence of mechanical effect and heat, of the 
“mechanical equivalent” by which the one may be con- 
verted into the other, or of the fraction of the heat which 
can be converted into work by a perfect heat engine. 
So far as it goes, in fact, the book is extremely clear and 
satisfactory ; but it gives one less impression of a com- 
plete working up of the subject to the latest date than we 
had expected to find in it. Take for instance the well- 
known series of experiments by which Kundt established 
the velocity of sound in tubes of different materials. 
They were explained by Tyndall in this country a couple 
of years since, and it is impossible to conceive any which 
make more visible to the student those vibrations of 
bodies which he is constantly required to admit in the 
course of his reading on acoustics. The omission of all 
mention of the famous “singing flames” is more defen- 
sible from a purely scientific point of view, as the experi- 
ments scarcely admit precise measurements, and can only 
be relied on to convince any one who needs convincing 
how many astonishing things there are within the range 
of the science. 
M. Fernet has given a considerable number of notes, in 
which there is a precise mathematical treatment of the 
statements in the text. We should be glad to see the 
plan followed more frequently in elementary treatises. In 
a book, the introduction of simple mathematics in a note 
does not distract the attention «{ the reader who is 
The | 

frightened even by a simple equation, and it gives 
precision to statements which can scarcely be fixed with- 
out them, or without a long and extremely tedious 
paraphrase. We are more doubtful of the advantage of a 
practice common in France, and which has crept into 
some English books; the introduction into the text of 
notes non exigées. These are parts which the student 
who is preparing for a special c::amination may omit if 
he chooses. The text of a book of this kind ought, it 
seems to us, to be either one thing or another—to be 
composed with a perfectly definite object, and to be one 
and indivisible. As it is, it produces something of the 
impression that is given occasionally when a single 
picture is used to illustrate two different propositions. 
The lines which belong to the first get so mixed with 
those of the second, that the student can follow neither. 
A book too full of motes non exigées is apt to be too little 
systematic and scientific for the more advanced student 
for whose benefit these notes are inserted, and to be 
made too difficult for the simpler readers whose wants 
are mainly kept in view. WILLIAM JAcK 


OUR BOOKSHELF 
Cryptogames Vasculaires du Brésil. Par Prof. A. L. Fée 
avec le concours de Monsieur le Dr. Glaziou. Pp. 268, 
4to., 78 Plates. (Paris: Bailliére.) 
PROFESSOR FEE is by many years the oldest amongst 
living fern-authors. He has held for more than a quarter 
of a century the chair of botany at Strasburg, and has con- 
centrated his attention principally upon ferns and the 
other allied higher orders of cryptogamic plants. He 
published a general treatise upon the classification of the 
order as long ago as 1844, and since then many consecu- 
tive years have never passed without producing some 
memoir upon the subject from his fertile pen. Having 
recently received a fine collection of ferns from Dr. Glaziou, 
the superintendent of the Botanic Gardens at Rio Janeiro, 
he has been stimulated to add one more memoir to the 
series, and that is the work now before us. All the series 
of his monographs, several of which are in folio, are illus- 
trated beautifully and copiously, not only with full-sized 
figures of the plants, but also with careful magnified ana- 
| lytical details ; and together they form by far the most ex- 
tensive and excellent series of fern-plates which anyone 
upon the Continent has published. The present memoir 
is quite upon a par with its predecessors in this respect. 
It is in quarto, and contains seventy-eight quarto pilates 
and a list of all the ferns and fern-allies known to the 
author as inhabiting Brazil, with a list of special stations, 
but with descriptions of novelties only, But there is one 
drawback to the value of Fée’s works, and that is a very 
great one. Living at a distance from the great metropoli- 
tan herbaria, our author has apparently worked a'most 
entirely upon his own private collections, and has continu- 
ally failed to recognise well-known plants, and has made 
new species in great numbers out of the specimens 
which his correspondents have sent him, which no one 
else has been able to understand as such. In none of his 
works—wehavenoalternative but to say—hasthis tendency 
been carried to a greater excess than in the present one. 
For Brazil alone he describes and figures in the present 
memoir upwards of 180 new species, so called. These are 
not from tracts of country which the collegtors whose 
gatherings have been already reported upon have not 
visited, or have left unexplored, but nearly all from the 
vicinity of the capital, and from the gatherings of Glaziou. 
Now the neighbourhood of Rio Janeiro is exceedingly 
rich in ferns; but there is, perhaps, no other part of Tropi- 
