34 NATURE 
| NOVEMBER 8, 1906 
detic survey in South Africa. 
With interest to the account of the various difficulties 
which had been met with in Africa. 
It is well known that the British South African 
Company, in fulfilment of the wishes of the late Mr. 
Cecil Rhodes, has up to the present year met all the 
heavy expense of that part of the survey along the 
thirtieth meridian of east longitude which runs 
through Rhodesia, but it has been found necessary for 
the company to effect various economies, and there 
was a doubt as to whether it might not prove neces- 
sary to suspend the survey for a time. Such a sus- 
pension would have proved most unfortunate, since 
there would have been no junction to the southward 
between the Rhodesian triangulation then completed 
as far as Gwelo and the Transvaal triangulation 
which begins at the Limpopo River. A surveying 
party under Captain Gordon, R.E., was already in 
the field in Rhodesia, and it was obvious that it 
would be much more economical to continue the 
work at once rather than to defer it until some 
undetermined time in the future. The expendi- 
ture needed for the survey from Gwelo to the 
Limpopo was estimated at 1600l., and after 
various negotiations in England the British South 
African Company offered to advance half that sum, 
while the Royal Society, the British Association (from 
a fund raised principally in South Africa for the 
meeting of 1905 at Cape Town and Johannesburg), 
the Royal Geographical Society, and Sir Julius 
Wernher subscribed the other half. These negoti- 
ations had to be conducted very hurriedly in order to 
obviate the break-up of the surveying party, but by 
means of the telegraph and through the exertions of 
Sir David Gill all obstacles were overcome, and 
Captain Gordon began work in June. Since the 
meeting of the geodetic conference I have heard from 
Sir David Gill that Captain Gordon is making good 
progress. Thus in a few months the triangulation 
will be finished up to and beyond the Zambezi. With 
respect to Northern Rhodesia, preliminary recon- 
naissance has been made nearly as far as Lake 
Tanganyika, and I have reason to hope that, although 
Sir David Gill is retiring from his position as Astro- 
nomer Royal at the Cape of Good Hope, the British 
South African Company will make arrangements for 
the completion of the great scientific enterprise for 
which they have already done so much. 
At Lake Tanganyika the continuation of the survey 
northward will fall to the Imperial German Govern- 
ment. The Academy of Sciences of Berlin has 
appointed a committee to consider the matter, and 
although Dr. Helmert was not able to announce that 
the work would be undertaken immediately, yet I 
think we may be confident that the northward pro- 
gress of the survey will be continued in a year or 
two. 
In Egypt Captain Lyons is making preparations for 
the geodetic survey southward, and I have no doubt 
that when the conference next meets substantial 
progress will be reported there also. 
In the years 1903 and 1904 the International Con- 
gresses of Geology and of Academies passed resolu- 
tions in which they asked for the help of the Geodetic 
Association in respect to accurate levelling and 
measurements of gravity with a view of throwing 
light on the internal distribution of masses in the 
earth and on the rigidity and isostasy of the crust 
of the earth. It was entrusted to M. Lallemand and 
to me to draw up preliminary reports on these sub- 
jects. M. Lallemand, whilst admitting the import- 
ance of the requirements of the geologists, could not 
maintain that levelling has attained to such a high 
degree of accuracy as to betray small movements of 
NO. 1932, VOL 75] 
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The conference listened 
the land relatively to the sea, but he thought that 
large changes of level could be detected, and he ex- 
pressed the opinion that the lines of levelling ought 
to be repeated at such intervals as two or three times 
a century. For my part I could not think that it was 
possible for geodesists to undertake such elaborate 
measurements of the direction and intensity of gravity 
as would fully satisfy the requirements of geologists. 
The repetition of the levelling of a country and 
systematic observations of gravity entail great ex- 
pense, and the conference seemed to be unanimously 
of opinion that they would not be justified at present 
in urging on their respective Governments any in- 
crease of expenditure in these directions. Neverthe- 
less, the wishes of the geologists will not pass . 
unnoticed, for there can be no doubt that in future 
campaigns with the level and the pendulum more 
attention will be paid than heretofore to the constitu- 
tion of the country under survey. 
Before referring to the resolution on this topic 
which was finally adopted by the conference, I must 
speak of two other communications of great import- 
ance. Mr. Tittmann, superintendent of the United 
States Coast Survey, and Mr. Hayford, inspector of 
geodetic work, communicated on behalf of the United 
States a very elaborate discussion of the anomalies 
of gravity throughout the United States. The con- 
clusions at which they arrived are of great interest 
to geologists, for it was shown by Mr. Hayford that, 
at least in the United States, the matter constituting 
the earth is in hydrostatic equilibrium at a depth of 
about seventy miles below the surface. In technical 
language, this is the depth of isostatic compensation. 
In this connection Baron Eétvés, professor in the 
University of Buda Pest, explained his application of 
the torsion balance or Cavendish apparatus for deter- 
mining local deviations from normality, both in the 
direction and in the intensity of gravity. His instru- 
ment, which we had the pleasure of seeing at the 
laboratories of the University, is of astonishing 
sensitiveness, and, so far as we can see at present, 
its indications are trustworthy. It would seem prob- 
able that this instrument might be used to give exactly 
those indications as to the distribution of internal 
masses of which the geologists are so desirous. The 
communication of Baron E6étvés was considered of 
so much importance that the conference directed 
special attention to it in the resolution which was 
adopted as an answer to the International Association 
of Academies. The Geodetic Association has at pre- 
sent no funds available for continuing researches with 
the torsion balance, but there is reason to believe that 
the Hungarian Government will continue to support 
Baron E6tvés in his researches. It may even become 
possible by measurements, say on Vesuvius, before 
and after an eruption, to find where the lava which 
is ejected from the crater has come from, since the 
displacement of large masses from beneath the moun- 
tain should be betrayed by the indications of the 
torsion balance. 
This meeting of the conference is the last under 
the existing convention, which expires at the end of 
the present year, but it was announced that twenty 
of the Governments which have taken part in the 
existing convention have already entered into a new 
one for the forthcoming ten years. There is reason 
to believe that the Argentine Republic will also join. 
Indeed, Dr. Porro was at Buda Pest as representative 
of that Republic, and took part in our discussions. 
A telegram has already appeared in the Times, and 
has been repeated in Nature, stating that I have 
invited the conference to meet in Cambridge in the 
year 1909. This is incorrect. It is true that the 
association has never yet met in England, and 1 
