506 
NATURE 
[April 27, 1871 
ee _ — 
of motion that a body, if moving, will continue to movein 
a straight line with uniform velocity, provided no forces 
act on it. There is through the whole book the most 
hopeless confusion as to what is meant by no forces act- 
ing. The author's theory of the cause of the moon’s mo- 
tion will illustrate the character of the book. It is briefly 
this :—If the moon were pulled only by the earth’s gravi- 
tation, it must fall to the earth, It must therefore be 
pulled in the opposite direction with an exactly equal force. 
‘This is called by the author the force of astral gravitation. 
Since these two exactly balance one another, the question 
arises, What can cause the moon to revolve round the 
earth? ‘A cause,” says the author, “ for the onward mo- 
tion of the moon according to the action of well-known 
laws, is, however, indicated by various well-known tidal 
phenomena. For the moon tends to raise a mass of water 
or tide on the earth’s surface beneath it ; and as the earth’s 
surface rotates eastward, it tends to carry that mass of 
water or tide with it; and therefore as the moon tends to 
hold the tide beneath it, the rotation of the earth eastwards 
must just as certainly tend to carry the moon eastwards 
as to carry the tide eastwards.” Really it is quite irritat- 
ing that such nonsense should be printed in large type, 
on good paper, and in a well-bound book. beds: 
It is one of the great merits of error that it is incon- 
sistent. That the author enjoys the full satisfaction of this 
merit is evident from the following :—“ If the moon and 
earth were at rest, then astral gravitation would tend to 
carry the moon directly from the earth, not at a tangent 
to any part of its orbit ; and when in motion, astral gravi- 
tation tends to carry the moon off at a tangent from its 
orbit certainly, but 2 the opposite direction to that of its 
motion at the moment of its being released from the grasp 
of the centripetal force.” The italics are the author’s—not 
ours. It appears from this that the author denies the 
second law of motion, as well as the first, which he else- 
where denies. He here assumes that the effect of a force 
on a body at rest can be at right angles to its effect on 
that body when in motion. It is much to be desired that 
those who undertake to write books would first learn the 
first principles of that which they write about. 
Catalogo FPoliglotto delle Piante. 
Contessa di San Giorgio. 
1870.) 
WE wish to call our readers’ attention to this interesting 
little volume. Its authoress will be better known in the 
country as Lady Harly of Oxford ; and she has spent 
many years in the compilation of this volume, which, we 
think, may prove useful to travellers on the Continent, 
and indeed, might even be made the means of instruction 
in our public schools. As an example, we select the Bed/is 
perennis, which, a native of Europe, we findis, in English 
Daisy ; French, Paquerette, Warguerite vivace, Fleur de 
vaques; Italian, Pratolina, Margheritina de Prati ; 
Spanish, Maya, la Margarita; German, Masslieben, 
Ginse Bliimchen, Angerblume, Osterbliimchen. But we 
find not only the European names of a large number of 
plants given, but, even in some instances, the Sanskrit, 
Bengal, Hind and Tamul names are also appended. 
Compilato dalla 
8vo., pp. i., 747. (Firenze, 


LETTERS TO THE EDITOR 
[Zhe Editor does not hold himself responsible for opinions expressed 
by his Correspondents, No notice is taken of anonymous 
communications. | 
Variability and Natural Selection 
I ASK your permission to address to your readers some obser- 
vations in support of the argument which Mr. St. George Mivart 
has adduced in his work on ‘‘ The Genesis of Species,” that 
Mr, Darwin has attributed too exclusive an effect in the origina- 

tion of new species to the influence of his law of Natural Selec- 
tion. 
1. There are two facts on which Mr. Darwin’s theory reposes 
—the one the variability of animal and vegetable forms; the 
other, the accumulation of a useful variation by force of the 
struggle for existence, or Natural Selection, Mr. Darwin 
assumes Variability to be accidental, not because he or any 
other philosopher supposes that there is such a thing as accident, 
but because its law is unknown. He then finds the law of 
Natural Selection, and by this and this alone, explains the 
Genesis of Species. 
Now, inasmuch as Natural Selection operates on Variabilily 
as a pre-existing fact, it follows that the genesis of a new species 
must result from the operation of two laws—namely, the law 
of Variability and the law of Natural Selection. But Mr. Dar- 
win attributes it exclusively to the latter ; so that, according to 
his view, there is a law (that of variability) which has no part 
in producing a result which yet depends for its existence on the 
fact regulated by that law—namely, variation. This is enormously 
improbable. _ It is as if the resultant from two factors were 
attributed exclusively to one of these factors. 
The fact that Mr. Darwin assumes variation to be accidental 
is, of itself, sufficient to make us expect some residual pheno- 
menon not accounted for by the law of selection: but Mr 
Darwin’s argument does not allow the existence of such a 
residuum. 
2. Mr. Mivart, following the orth British Review, has 
shown the great advantaye in the struggle for existence which 
the numerical superiority in individuals of the original form over 
the new variation may give to the original form. I want to call 
your attention to the fact, that the useful variety has tv overcome 
not only this advantage to its antagonist resulting from numbers, 
but a quite distinct difficulty, namely, the tendency to reversion ; 
or, that in other words, the force which Mr. Darwin has at his 
disposal is not the tendency to accumulate a variation, but only 
the balance of this tendency over the tendency to reversion. 
It is no doubt difficult to estimate the extent to which one ten- 
dency is controlled by the other ; but to gain some notion of it, 
let me assume the existence of three forms, with a male and 
female of each, viz., 
male female 
a a’ the original form 
b 2 the first variety 
c c’ the second variety 
Let me further indicate the existence of an accumulated variation 
by the double letter 44, or cc. Let me thea assume an equal 
chance of sexual intercourse between each of the six individuals 
and of progeny from such intercourse, aud we shall see what are 
the chances of the origin of an accumulated form. For the 
union of 
a and a’ produces @ 
a ” u ” a 
ke omnia Co 3 a 
b Su ie s a 
=4 
: ” ur ” bb 
c a 
: ” al ” 2 
” »” 
c ” u »” a 
Ce ee a cc 
So that in the first generation the chance against any given ac- 
cumulated variation being produced are 8 to 1, and the chances 
against any accumulated variety at all being produced are 7 to 1 ; 
and these odds will go on increasing, because the next generation 
will retain the tendency to revert to the original simple parent 
form a, not to the original forms of the last preceding generation 
only. If I assume that each marriage in the first generation 
produced two males and two females, the result will be, that in 
the second generation the chance against any given accumulated 
variety being produced will be 320 to 4 or 160 to 2; and the 
chance against any accumulated yariety at all being produced 
will be 316 to 8 or 79 to 2. 
These chances express the force of the tendency against which 
Natural Selection has to operate, assuming that the numbers of 
each variation at starting were equal to those of the original form ; 
but this is, on the assumption that variation is accidental, in 
finitely removed from the truth; and if the difference betwee. 
the numbers of the original form and the variation be introduced 
into the case, the odds are indefinitely increased against the ac- 
cumulation of a casual variety. None of these observations 
goes to show that Natural Selection does not exist (I have 
