= 
» . 
in Asal an 
Cee ee ee 
aes, 
Sept. 4, 1873] 
regretted, as there are two well-known works to which 
the epithet is fairly applicable, and which are at least 
free from such erroneous facts and false or exploded 
theories as have been pointed out in Dr. Page’s volume. 
ALFRED R. WALLACE 
OUR BOOK SHELF 
Half-hours in the Green Lanes: a Book for a Country 
Stroll, By J. E. Taylor. (Hardwicke.) 
THERE are two ways at least in which the first principles 
of Natural Science may be taught to the youthful mind, 
as well as to “intelligent people who have not had time to 
enter into the technicalities of scientific questions.” One 
which, if we may judge from the number of elementary 
works on Physics in which it is adopted, has many argu- 
ments in its favour, consists in the careful and logical 
working out in detail of a few of the most important prin- 
ciples of the Science, together with the different steps by 
which they were arrived at ; the knowledge of minutize 
being left for future observation and study, on the foun- 
dation supplied: and the other is little more than a 
compilation of disconnected facts, of unequal importance, 
arranged with an endeavour to make them impressive 
from their almost endless number, and strung together 
with teleological argument. The tenants of the “tarns 
and green lanes being the objects treated of, there is an 
expanded field for the 300 or so short pages, in which the 
fishes, molluscs, and reptiles of the former, as well as the 
birds, insects, and plants of the latter, are rapidly passed 
in review. Several excellent figures illustrate the work, 
Mr. Wood and Mr. Keulemans contributing to the orni- 
thological section ; however, we are surprised to see so 
many on subjects of comparatively little importance, as 
the 14 on the slight variations in the shape and marking 
of cycloid scales, and the 32 on the different species of 
snails. Turning to the letterpress, many of the descrip- 
tions will be found to be accurate and clear, and a few 
sufficiently long to enable the uninitiated to form a fair 
idea of the subject. Many however are so short and in- 
complete that but little can be made of them without 
extraneous assistance, and in some the carelessness in 
the choice of words adds to the difficulty, as where the 
Vapourer Moth (Orgyia antigua) is said to derive its 
name “from the habit of the winged males rising and 
falling simultaneously in their flight.” A fact is some- 
times stretched to make a szmz/e, as when we are inaccu- 
rately told that “the generic name of the Kingfisher 
(Halcyon) is derived from the ancient belief that when 
it was hatching its eggs, the water was always calm and 
still.” The genus Zz7dus is more than once called Tardus, 
and several other mistakes show that the authors know- 
ledge of the subject is not of the deepest, as when the 
hind wing of the Clifden Nonpareil (Catocala fraxini) is 
said to be black and red, and the wide geographical dis- 
tribution of the Kingfisher is given as a reason for sup- 
posing that it has a comparatively high geological antiquity. 
Notwithstanding its faults, however, there are many points 
in this small work which will make it of more than ordi- 
nary interest to the general reader. 
The Royal Readers. Nos. 1 to 6. (Nelson and Sons, 
London and Edinburgh.) 
THE excellence of these reading books and their adap- 
tation to the broader culture of the present day demand 
from us some notice. The editor of the series, who has 
done his work with unusual ability, tells us in the preface 
that his aim has been to cultivate the Jove of reading. So 
far as we are able to judge, this aim he has successfu!ly 
carried out by presenting interesting subjects in an at- 
tractive way. Opening any one of these Readers, we are 
struck with the air of freshness and interest it possesses. 
NATURE 
361 
An intelligent child, instead of closing the book with 
relief, is far more likely to leave it with regret. And added 
to the happy way in which the lessons have been prepared, 
the pages abound with capital woodcuts, some of which 
are of real beauty. There are none of the stereotyped 
cuts of stale children in old-fashioned dresses and hair in 
pig-tails, primly grouped at play, and supposed to illus- 
trate the story of the goody-goody girl, or the naughty- 
naughty boy, Our children are mercifully spared from 
these haunting ghosts of our childhood and have their 
Royal Readers instead. But these books have a wider 
scope than mere reading lessons. In the fifth and sixth 
books we find a large amount of sound scientific know- 
ledge conveyed in a course of lessons carefully prepared 
by the editor. Then there are articles on physical geo- 
graphy, the bed of the sea, the various ocean routes, and 
lessons on useful inventions, besides some other novel 
features which we have not room to detail. The employ- 
ment of these reading books will certainly tend to create 
a love for healthy reading, and at the same time they 
seem likely to be of the highest service in training and 
furnishing the minds of children. 
LETTERS TO THE EDITOR 
[Zhe Editor does not hold himself responsible for opinions expressed 
by his correspondents. No notice is taken of anonymous 
communications. ] 
Atoms and Ether 
I AM not enough of a metaphysician to say whether a sub- 
stance which can be compressed and expanded mecessarily con- 
tains void spaces. 
If so, the idea of air, furnished to a beginner by instruction in 
“Boyle’s Law,” is self-contradictory ; and any molecular theory 
afterwards developed in order to account for ‘‘ Boyle’s Law,” 
may claim not only ingenuity but necessity in order to abate a 
crying grievance to all right-minded persons. 
I do not myself believe in Prof. Challis’s zther, but at the 
same time I do not believe in the power of the human mind 
to pronounce that a continuous medium capable of being com- 
pressed is an impossibility. 
But, on the other hand, Iam sure that a medium consisting 
of molecules is essentially viscous; that is, any motions on a 
large scale which exist in it are always being converted 
into molecular agitation, otherwise called heat, so that every 
molecular medium is the seat of the dissipation of energy, 
and is getting hotter at the expense of the motions which it 
transmits. Hence no perfect fluid can be molecular. So far as 
I can see, Prof. Challis intends his ether to be a perfect fluid, 
and therefore continuous (see p. 16 of his Essay), though he 
does not himself pronounce upon its intimate constitution. 
Hansemann* makes his xther molecular, and in fact a gas 
with the molecules immensely diminished in size. 
With regard to Mr. Mott’s iron bar, when he pulls one end he 
diminishes, in some unknown way, the pressure between the 
particles of the iron, and allows the pressure of the zther on the 
other end to produce its effect. 
N.B. This is only the language of a theory, and that theory 
not mine ; nevertheless, I think it isjconsistent with itself. 
Glenlair, Aug. 13 JCM 
Reflected Rainbows 
I READ with great interest, in Prof. Tyndall’s American lec- 
tures, a statement about the rainbow which appeared to me so 
extraordinary, that I determined to test it on the first oppor- 
tunity. 
The statement (I have not the took with me here, and give 
merely my recollection of the substance) is that, owing to the 
want of the necessary condition of parallelism the rays scattered 
from rain-drops cannot be so reflected as to show a rainbow by 
reflection from the surface of a lake. 
Of course we all know that the same rainbow cannot be seen 
from two places at the same time, and therefore no one would 
* Die Atome und ihre Bewegungen, von Gustay Hansemann, E, H 
Mayer: Coln, 1871.) 
