Sune 29, 1871] 
If this is done at all thoroughly, the modes of expressing 
the laws of physical phenomena in technical mathematical 
language may almost be left to suggest themselves when 
the requisite progress shall have been made in pure mathe- 
matics. 



BOOK SHELF 
The Sub-tropical Garden; or Beauty of Form in the 
Flower-Garden. By W. Robinson, F.L.S. With Illus- 
trations. (London: Murray, 1871.) 
THIS volume is a sequel to the valuable works which Mr. 
Robinson has already given us—“ The Wild Garden,” 
and “ Alpine Flowers for English Gardens.” The title is 
a misleading one, and is thus dcfined by the author :— 
“ Sub-tropical gardening means the culture of plants with 
large and graceful or remarkable foliage or habit, and the 
association of them with the usually low-growing and bril- 
lint flowering-plants now so common in our gardens, and 
which frequently eradicate every trace of beauty of form 
therein, making the flower-garden a thing of large masses 
of colour only.” It is a pity that Mr. Robinson has 
assisted to perpetuate so erroneous a designation, which 
conveys the idea of the culture of tender plants fitted only 
for our hothouses. The greater part of the volume is 
occupied with an alphabetical list of plants suitable for 
the above purpose, with description of the peculiarities of 
their foliage, mode of cultivation, and propagation, &c. 
The accompanying cut is intended to suggest the effects 
to be obtained from young and vigorous specimens of 
hardy, fine-leaved trees. Inall these points Mr. Robinson 
AILANTUS AND CANNAS 
may be safely followed as a guide, combining great prac- 
tical knowledge of gardening, an extensive acquaintance 
with the native habits of plants, and an artist’s eye to the 
beauty of form andcombination. The following sentence 
gives his idea of what gardening should be. “ Nature, zz 
puris naturalibus, we cannot have in our gardens, but 
Nature’s laws should not be violated ; and few human 
beings have contravened them more than our flower-gar- 
deners during the past twenty years. We should com- 
pose them from Nature, as landscape artists do. Wemay 
NATURE 


E59 

have in our gardens, and without making wildernesses of 
them either, all the shade, the relief, the grace, the beauty, 
and nearly all the irregularity of Nature.” A. W B. 
The Meteoric Theory of Saturn's Rings, considered with 
Reference to the Solar Motion in Space; also a paper 
on the Meteoric Theory of the Sun. By Lieut. A. M. 
Davies, F.R.A.S. (London: Longmans & Co.) 
PROF. CLERK MAXWELL, in his remarkable essay 
“On the Stability of Saturn’s Rings,” which gained the 
Adams Prize in 1856, exhaustively examines the various 
theories of the constitution of these rings, and decides 
what are the impossible mechanical conditions for their 
maintenance and what is the possible one. He shows 
that they cannot be solid or rigid; he disposes of the 
possibility of their being continuously fluid, and he con- 
cludes that “‘the only system of rings which can exist is 
one composed of an indefinite number of unconnected 
particles revolving round the planets with different velo- 
cities according to their respective distances.” Lieut. 
Davies appears not to have seen Prof. Maxwell’s work, as 
he ascribes to the perusal of a derived exposition of it the 
enlistment of his interest in favour of the Satellite theory 
of the rings. Having espoused this theory, he has sought 
an explanation of Saturn’s possession of a ring system in 
the supposition that the planet has picked up streams of 
meteors inits path through space ; this path being a spiral 
resulting from the planet’s orbital motion in conjunction with 
the proper motion of the solar system. The spirals traversed 
by the four planets beyond Mars are projected in accord- 
ance with Lieut, Davies’s assumption of the solar motion, 
in order to show that Saturn is (excepting Jupiter) more 
favourably circumstanced than other planets for encoun- 
tering wandering streams of meteors that are drawn 
towards the sun ; while, from consideration of the masses 
and the distances of the two- planets from the sun, it is 
argued that Saturn is better circumstanced than Jupiter 
for attaching such streams permanently to his system in 
the form of rings. The details of Lieut. Davies’s work can 
only interest those who are closely concerned with cos- 
mical hypotheses. We will merely remark that he appears 
to place too great faith in figures : he gives the hourly rate 
of the solar motion in space toa mile, and quotes the solar 
parallax to four places of decimals! The velocity is avery 
uncertain element of the solar motion, and a small altera- 
tion of the rate assumed by Lieut. Davies would greatly 
modify his conclusions. The book includes a paper on 
the meteoric theory of the sun, a theory with which the 
author is blindly enraptured. He claims that it “accounts 
for every phenomenon hitherto observed on the solar 
surface.” He holds that the “ willow leaves” are meteoric 
flights just falling into the sun ; that the spots are spaces 
upon which no meteors are raining ; that the periodicity 
of spots is due to the action of the planets in pulling “the 
meteoric matter outwards from the surface of the sun into 
Jarger orbits, thus temporarily delaying its precipitation,” 
and that “the form of the spots bespeaks their origin as 
extraneous to the solar machinery. Were they cyclones 
in the atmosphere, they would invariably present a rotatory 
appearance 0 This must result were the origin 
of the spots in a plane parallel to the tangential plane at 
the sun's surface ; but would not do so if their origin lay 
in the normal to that plane, as it does in the meteoric 
theory. A careful study of Mr. Carrington’s valuable series 
of observations of solar spots is decidedly unfavourable to 
the conclusion that they have forms of rotation.” Lieut. 
Davies is either innocently or wilfully ignorant of the pal- 
pably cyclonic appearance which spots frequently present, 
and which has been frequently depicted by observers who 
have studied the characteristic features of individual spots. 
This study did not concern Mr. Carrington. The devotees 
of the meteoric theory of the sun’s maintenance will not 
feel that it has been much advanced by Lieut. Davies’s 
over-straining advocacy. 
