Fan. 12, 1882] 
stated one would also be sent by Spain: the duplication 
of stations is not desirable in suchacase. The Presi- 
dent’s propositions were adopted, but in addition the 
Committee on Methods was also charged with the con- 
sideration of the calculations and publication of the ob- 
servations in 1882, and were further deputed to consider 
the formation of a temporary international bureau, to be 
intrusted with the reduction of the whole of the observa- 
tions. At the fifth and last sitting of the Conference on 
October 13, the report from the Committee on Methods 
of Observation, &c., was presented. The proposals 
of the British Commission respecting the phenomena 
to be noted at the contacts of the limbs of the 
sun and Venus, brought forward by Mr. Stone, 
were made the foundation for a series of instruc- 
tions to observers, some explanations being appended 
thereto. After much divergence of opinion with regard 
to the advantage of an international dureau des calculs, 
the following proposition introduced by M. Dumas, and 
supported by Mr. Stone on the part of the English com- 
mission, was adopted by a large majority. 
“The Conference expresses the wish that the French 
Government may be willing to communicate in diplomatic 
form with the other governments represented in this con- 
ference, or those who are interested in the transits of 
Venus, in order to lay before them the proposition of 
convoking, after the return of the expeditions of 1882, an 
international conference on the transits of Venus, with a 
view to establish an understanding on the means to be 
adopted to arrive at the best and most expeditious use of 
the observations of the transits of 1874 and 1882, and in 
particular to inquire whether towards this end a tem- 
porary international bureau should not be formed.” 
The report closes with a list of the projected stations 
for the expeditions, so far as at present arranged. The 
British stations selected are:—Bermuda, Jamaica, Bar- 
bados, Cape Colony (3), Madagascar, New Zealand, 
Falkland Islands (?), with the Australian observatories, 
ON THE PHYSICAL CAUSE OF THE OCEAN 
BASINS 
EOLOGISTS have reason to thank Prof. Ball for 
directing their attention to the remarkable investi- 
gations of Mr. G. H. Darwin upon “‘ The Precession of a 
Viscous Spheroid, and the Remote History of the Earth,” 
(Phil. Trans. Roy. Soc., Part ii., 1879). Prof. Hull has 
already been led to point out one result which appeared 
to him to flow from them, in showing how the ancient 
tides may have produced the planes of marine denuda- 
tion, though Mr. Darwin has since expressed doubts as to 
the legitimacy of this conclusion. I wish to offer another 
speculation arising from Mr. Darwin’s work, which I 
think may account for the hitherto unexplained distribu- 
tion of land and water upon the surface of the globe. 
Herschel remarked long ago, in his ‘‘ Physical Geo- 
graphy,” that the prevalence of land and water over two 
opposite hemispheres “proves that the force by which 
the continents are sustained is one of ¢umefaction, inas- 
much as it indicates a situation of the centre of gravity 
of the total mass of the earth somewhat eccentric rela- 
tively to that of the general figure of the external surface 
—the eccentricity lying in the direction of our antipodes : 
and is therefore a proof of the comparative /Zghtness of 
the materials of the terrestrial hemisphere.” In my 
“Physics of the Earth’s Crust,’’ just published, I have 
shown reasons for thinking that the distribution of the 
materials of the earth, which gives rise to this condition, 
is of the following kind. 1 accept on the whole the 
theory that the earth is a hot globe, of which the super- 
ficial crust is rendered solid by having become cool, and 
that the central part is solid, either from great pressure, 
or from whatever other cause may be assigned ; an inter- 
vening layer beneath the cooled crust still remaining 
NATURE 
243 
liquid. The layers of which the whole is composed are 
arranged in order of their density. Now I have given 
reasons for believing that Herschel’s ‘‘ comparative light- 
ness of the materials of the terrestrial hemisphere ”’ 
arises from the fact that the cooled crust beneath the 
continents is intrinsically less dense than that beneath the 
great oceans. I think that the crust beneath the conti- 
nents consists of the cooled acid, or granitic, and there- 
fore lighter magma, which ought naturally to have formed 
originally the entire superficial portion of the globe. But I 
conclude that the bottoms of the great oceans consist never- 
theless of a crust formed out of the cooled basic layer. Be- 
neath the cooled crust the laws of hydrostatic equilibrium 
would require that, if the substratum is truly liquid, it should 
be of the same density under both these areas. I also con- 
clude that the upper surface of the basic crust which 
forms the floor of the oceans is really depressed below 
the mean surface of figure. 
To these conclusions I arrived without being able to 
suggest any satisfactory explanation of the facts. I saw 
that they agreed with, and were supported by, the view of 
those geologists who assert that the great oceanic and 
continental areas have never changed places ; but neither 
could I any better see the reason for this. 
Let us now inquire whether Mr. Darwin’s researches 
throw any light upon the subject. I shall refer chiefly to the 
summary and discussion of results appended to his paper, 
for it is small blame to a sexagenarian, not a professed 
mathematician, to admit that to follow the calculations is 
beyond the scope of his powers. As I understand Mr. 
Darwin, he thinks it probable that the moon and the 
earth were once a single mass, and that at the time when 
this mass was rotating at the rate of about one revolution 
in five hours the whole separated into two portions, the 
smaller of which went to form the moon; and that the 
moon then began to recede from the earth, until now, 
after the lapse of fifty-four millions of years 07 more, it is 
at its present distance. The ellipticity of the mass when 
rotating at the above-named speed would be about 1-12th. 
[This would make the mass very much less compressed 
than an ordinary orange.] He does not think it probable 
that this amount of ellipticity would cause the spheroid 
to break up simply from the centrifugal effect of the rota- 
tion; but he suggests, judging from the calculated period 
of a gravitational oscillation of a fluid spheroid, of uni- 
form density equal to the mean of the earth, viz. I hour 
34 minutes, that the period of the free oscillation of a 
spheroid “consisting of a denser nucleus and a rarer sur- 
face,” but of the same mean density as the earth, might 
coincide with the period of the bodily solar tide at that time. 
“Tt seems to be quite possible that two complete gravita- 
tional oscillations of the earth in its primitive state might 
occupy four or five hours.” “‘ Accordingly the solar tides 
would be of enormous height.’’ He then adds: “ Does it 
not then seem possible that, if the rotation were fast 
enough to bring the spheroid into anything near the un- 
stable condition, then the large solar tides might rupture 
the body into two or more parts? In this case one 
would conjecture that it would not be a ring that would 
detach itself.” 
I now proceed to build my speculation upon his. It is 
obvious that, according to the above theory, the act of 
fissiparturition by which the moon was born must have 
been sudden. One of the two solar tidal protuberances 
broke away from the earth to inchoate a separate exist- 
ence. A great but shallow hole must consequently have 
been formed, whose centre would have been on or near 
the equator. Prof. Ball says: “ Not for long would that 
fragment retain an irregular form ; the mutual attraction 
of the particles would draw the mass together. By the 
same gentle ministrations the wound on the earth would 
soon be healed. In the lapse of time the earth would be- 
come as whole as ever, and at last it would not retain 
even a scar to testify to the mighty catastrophe.” 
