ri 
ar 
* 
cpt. 4, 1873] 
dimension expressed in different ways, must be propor- 
tionate in any two planets ; yet we have Mercury, volume 
006, solid contents 10°195 ; Venus, volume 096, solid 
contents 223'521, so that while the volume of Venus is 16 
times that of Mercury, its solid content is 22 times! 
Again: Earth, volume 1’00, solid content 260°775 ; Mars, 
yolume 0'14, solid content 48'723, the earth being over 7 
times the volume of Mars, but only 53 times its solid con- 
tent. Almost any other two planets come out equally 
wrong. Again, from the diameters given the solid con- 
tents can be easily calculated, but here again is frequent 
error ; and to add to the confusion, in at least two cases 
the diameters are seriously wrong (4,980 miles instead of 
4,100 for Mars, for instance), so that it is very difficult to 
understand where so many mistakes could have come 
from. On the next page we have a contradiction as to 
the earth’s internal structure. It is first stated positively 
that “the interior of the earth cannot be composed of the 
same materials that constitute its outer portion,” and 
lower down, that “ either the interior of the earth is com- 
posed of materials differing altogether from those known 
ae, 
- 
_at the surface, or the compression must be counteracted,” 
&c. At page 27 we have the atmosphere described as 
“mainly composed of two gases, nitrogen and oxygen— 
79 parts of the former to 21 of the latter—with a small 
percentage of carbonic acid and other extraneous impuri- 
ties.” Considering the importance of the carbonic acid 
gas in the atmosphere, it is hardly instructive to class it 
as an “extraneous impurity.” 
Passing over the mere description of the earth’s surface, 
parts of which arevery well done, we find other objectionable 
matter as soon as we have to deal with the explanation of 
phenomena. A mountain range is said at p, 75 to be 
“not a simple upheaval, the result of one paroxysmal 
outburst, but the work of innumerable volcanoes and 
earthquakes operating through ages and subsequently 
escarped and chiselled by rains, frosts,” &c. Here gra- 
dual elevation without volcanoes or earthquakes, and 
possibly from altogether different causes, is ignored. On 
the next page, speaking of circumdenudation, we have :— 
« A mountain may thus consist of stratified rocks and be 
-wholly unconnected with any forces of upheaval or ejec- 
tion from below.” Here ignoring that the strata must be 
upheayed before they can be circumdenuded. These are 
perhaps slight matters, but we think an introductory work 
should not adduce the almost exploded theory of Elie de 
Beaumont on the parallelism of mountain chains of the 
same age, “ even when in opposite hemispheres,” as if it 
were generally admitted, or Prof. Hopkins’ explanation of 
central mountains with diverging spurs as the result of 
an upheaying force acting on a point, without stating that 
a very different explanation of the facts is adopted by 
most modern geologists. 
When we come to the subject of the ocean, involving 
many nice problems in physics, our author is again alto- 
gether at fault. It seems hardly credible that he should 
not know the difference between salt and fresh water as 
regards the point of maximum density, on which much of 
the theory of oceanic circulation and temperature de- 
pends; yet such seems to be the case. At p. 123 weare 
told that “at 40° Fahr. water is at its minimum volume 
and maximum density,” and again in the same page— 
“Tts maximum density or minimum volume at 39}, its 
NATURE 
359 
expansion as ice to one-ninth of its bulk at 32° for fresh 
water and at 28} or less for salt water.” Again, at p. 131 
we have—“As already mentioned, water acquires its 
minimum volume or greatest density at a temperature of 
40°, and becomes lighter as it rises above or falls below 
this temperature. Owing to this property a perpetual 
interchange or circulation is kept up among the waters of 
the ocean,” proving that sea-water also is supposed by the 
writer to have this property, instead of increasing in 
density down to about 274°, as it actually does. Yet the 
author quotes Maury, who published this correction of 
the old notion in 1861, and the papers of Dr. Carpenter, 
who repeatedly refers to this fact as a most important 
one. Again, at p. 136 we have the obsolete theory of Sir 
James Ross as to deep-sea temperatures given in full, 
with a remark that it has recently “ been materially inter- 
fered with” by the experiment of Drs. Carpenter and 
Wyville Thomson ; but without, apparently, any acquaint- 
ance with the whole of the facts established by those gentle- 
men, as shown by again referring to the temperature of 
the bottom of the ocean as being 39° Fahr., “that of its 
maximum density.” 
It is perhaps a small matter that, in describing the 
Nile valley, Capt. Speke’s account is quoted at length (p. 
181), and the Victoria Nyanza given as the source, the 
Albert Nyanza not being once mentioned, or any 
allusion whatever made to the fact that Sir Samuel Baker 
claims it to be the true source of the Nile; but it is of 
great importance that the student should be impressed 
with clear and accurate ideas as to the cause of winds. 
Yet we find here the old school-book notion of a vaccum 
and an inrush to fillit up. “As air is expanded by heat 
and contracted by cold the warmer and lighter volumes 
will ascend, and the colder and denser rush in from all 
sides to supply the vacancy” (p. 205). ‘The air of the 
torrid zone becomes rarefied and ascends, while the colder 
and denser air sets in from either side to supply the defi- 
ciency” (p. 213). And the same words are repeated at p. 
243. But every physicist knows that there is no “va- 
cancy” and no “deficiency” in the case, but merely a 
disturbance of equilibrium; and unless this is clearly 
comprehended the causes and effecis of atmospheric 
currents can never be understood. On the subject of 
light and heat the ideas of the author appear to be still 
more confused. At p. 205 he says—“ As the atmosphere 
is the medium through which the sun’s heat is conveyed 
to and disseminated over the earth, so also it is the me- 
dium of his light-giving rays.” This sentence will cer- 
tainly convey to the learner the false notion that the at- 
mosphere is in some way essential to the ‘‘ conveyance’ 
of light and heat from the sun to the earth ; and this is 
further dilated upon in the following vague and unintel- 
ligible, if not erroneous sentence :—“ Heat and light are 
alike indispensable to plants and animals, and, from the 
peculiar constitution of the atmosphere, as regards its 
varying density, moisture, &c., both are reflected and 
diffused so as to become most available to vegetable and 
animal life.” The learner must be very acute who can 
obtain ary definite information from such oracular teach- 
ing as this. Again (at p. 207) we have a total misconcep- 
tion as to the cause of the decrease of temperature at in- 
creasing elevations—“ The heat that falls on the land 
being partly absorbed and partly radiated into the atmo- 
