Page 363

Mar. 7, i872]
NA TURE
calculation. The future must show how far it will be
possible to apply to the theory of species the definition
of central specific forms, from which varieties calculably
diminish in numbers as they depart in type.
                                        E. B. TVLOR
                OUR BOOK SHELF
Ma g-tism.e By Sir W. Snow Harris and H. M. Noad.
             (London: Lockwood and Co.)
THiS is a good book, and we are glad to see the subject
of magnetism fully treated in a popularly written text-book.
It is a second edition of Sir William Snow Harris's
rudimentary treatise, with considerable and important
additions by the editor. The part of chief importance
which is added is Chapter viii., which deals with the more
recent progress of terrestrial megnetism. This chapter
consists of thirty pages, and the author has managed to
condense into that space a wonderfully large amount of
interesting, useful, and accurate information on the
subject. In so short a space we must be content with
results rather than with particulars, but the matter con-
tained in this chapter, in point of importance, accuracy,
and exhaustiveness, places the present treatise, as far as
terrestrial magnetistn is concerned, m-ich before any
similar book with which we are acquainted. The correc-
tion of the com:ass in iron ships is entered into in the last
chapter. The telegraph is scarcely touched upon, but
this perhaps rather belongs to a treatise on electricity.
We have a chapter on theories of terrestrial magnetism.
The theory of Gauss should never be classed, as it is here,
and indeed as it is generally classed, along with theories
like those of Halley or Hanstein, or with such things as
electro-magnetic theories and the like. The word " theory"
in these cases means quite a different thing from what it
means when applied to Gauss's investigations. Hanstein
and the like all make some physical hypothesis, which
may or may not be the case ; but Gauss makes no such
assumption at all, except in so far as he supposes that
the needle at all parts of the earth's surface is affected by
forces due to the same origin, and varying inversely as
the square of the distance, which has been experimentally
proved to be the law according to which magnetic forces
act. He then shows how the effect on a needle can be
expressed in termis of an infinite series which is neces-
sarily mathematically convergent and true, and he then
uses an approximation to that series, which approxima-
tion is justified fully by experiments similar to those made
by the late Prof. Forbes at the top and bottom of the
Faulhorn.   Gauss's theory, then, is a truly scientific
theory, inasmuch as it involves no unjustified physical
hypothesis, but is a logical deduction from observed facts
and established principles, and in this differs radically
from the other theories which are too often classed with
it. Dr. Noad has been so successful in Chapter viii. that
we cannot help wishing he had introduced a chapter also
on this subject.                      JAMES STUART
The Amateurs Flower-Gardez : a Handy Guide to the
  Formation and Management of the Floower Gardenz
  and the Cultivztion of Garden Flowers. By Shirley
  Hibberd. Illustrated with coloured plates and wood
  engravings. (London: Groombridge and Son, 1871.)
AIR. HIBBERD is a practised writer on gardening subjects,
though his books have not much claim to be considered
as scientific treatises, bit rather as pretty gift-books to lie
on the drawing-room table and give to its furniture a
quasi-scientific air. That they have their use cannot be
doubted, but it is not a very high one.  The worst
part of this book is the illustrations. From the letter-
press may be doubtless culled some useful hints as
to the planting and management of a flower-garden,
though we do not think it equal in this respect to some
other wvorks, such as those by Mr. Robinson, which are
less under the trammels of time-honoured prejudices and
superstitions. But many of the illustrations, including
some of the woodcuts and nearly all the coloured plates,
are simply atrocious. The drawings of a show pelargo-
nium (p. 8o), pansy (p. 45), ranunculus (p. 156), carnation
(P. I [ 7), and some others, are mere caricatures, and un-
worthy of a place in any work which bears the least
pretensions to a scientific character.
         LETTERS TO THE EDITOR
[The Elitor does not hlul himself responsible jor opinions expressed
    by his correspon.dlents.  No notice is taken of anonymous
    communications. ]
             The Survival of the Fittest
  I HAD designed sending a note to you, critical of the abstract
of my paper on " The Laws of Orgaiic Development," repub-
lishel from the American Nraturalist in one of your recent issues,
before I reLd the remarks of Mr. Spencer in your number of
February i.
  If Mr. Spencer will examine the Essay itself (for sale by
McCalla and Stavely, 237, Dock Street, Phila., or Naturalists'
Book Agency, Salem, Mass.*) he will find that I have there ex-
clusively employed his phrase " Survival of the Fittest." The
expression "Preservatioa of the Fittest," not used by Mr.
Spencer, was inadvertently introduced in writing the abstract.
This was done hurriedly between the sittings of the Amer. Assoc.
Adv. Sci for a reporter of the Nlez York T)-ibune, and was sub.
sequently printed by the Naturalist while I was absent on th-
Plains of Kans is. It therefore contains several obscurities, the
result of an attempt to abridge, and a number of typographical
blunders. The essay will be found to be free from these.
  There being no misrepresentation of Mr. Spencer's views on
this point, I notice the second objection he makes. Where, in
the sentence regarding the Survival of the Fittest, I say that
"this neat expression no doubt covers the case, but it leaves
the origin of the fittest entirely untouched," Mr. Spencer re ,ards
my language as an " indirect statement that I " (Mr. S.) "have
done nothing to explain the origin of the fittest."
  It i, plain enough that my remark does not apply t3 Mr.
Spencer or to his writings, but exclusively to the doctrine of
Natural Selection, and to Mr. Spencer's terse phrase, "which
no doubt covers the case," i e. Natural Selection (not the whole
theory of Evolution). I cannot see that this language can be
tortured into the interpretration Mr. Spencer places upon it, but
Mr. Spencer's language decidedly implies that my statement is
literally correct.
  I am, however, well aware that Mr. Speacer has done more
than any living man to explain the " Origin of the Fittest," and
on this account in particular his name does not appear in my
criticism. Another reason for its omisiion is that I have taken
the liberty not to read his work, " The Principles of Biology,"
because I have suspected, from my reading of other works of this
philosopher, that it is in advance of oher treatises on the subject.
I postponed it until, by investigation " in the shop," I should
have attained to some definite views based on reasonin- un-
influenced by the opinions of others, hoping to use  "The
Principles of Biology" thereafter in such a way as its merits
and justice to its author shuald require.
                                     EDWARD D. COPE
  Philadelphia, Feb. 20
              Ethnology and Spiritualism
  THERE is only one point in Mr. Tylor's communication
(NATURE, Feb. 29, p. 343) on which it seems desirable that I
should say a few words, in order that I may not be supposed to
assent to what I conceive to be a most erroneous view. Mr.
Tylor suggests that the phenomena that occur in the presence of
what are called mediums, are or may be of the same nature as
the subjective impression; of persons under the influence of a
powerful mesmeriser.  Five and twenty years ago I was myself
    * Under the title, " The Method of Creation of Organic Types."
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