1906.] on International Scipjice. ?>bl 



of measuring this arc is well in hand, though at the present moment, 

 want of funds threatens to endanger its completion. The Egyptian 

 survey entrusted to Captain Lyons will no doubt receive continued 

 support, and by an arrangement entered into ])etween representatives 

 of the German Government and Sir David Gill at a Conference held 

 in Berlin, in 1S1)6, Germany undertook to carry out the triangulation 

 through her territory in South West Africa. 1 understand this work 

 has been done and the triangulation of the Transvaal and the Orange 

 River Colony is also complete. There is still a gap in the southern 

 part of Rhodesia, but there is every hope that this will soon be 

 bridged over. The British South African Company ha^e spent 

 36,000/. on the work and thus have very materially assisted an im- 

 portant enterprise. When the African arc is complete it will be 

 connected with the Russian and Roumanian arcs so as to form a 

 continuous chain of 105° extending from 70° north to 35° south 

 latitude. I have to point out, however, that in the opinion of those 

 best able to judge, the completion of the South xifrican arc is not the 

 only undertaking to which this country is called upon to pay atten- 

 tion. The triangulation of our own island, excellent as it was when 

 first made, has fallen below the accuracy required in modern geodetic 

 work. Until our fundamental triangulation has been repeated the 

 sums which at present are being spent on the detailed survey might 

 find a better use. 



The main result of the work has been that so far as j)resent 

 measurements allow us to judge, the surface of the ocean can be well 

 represented by a surface of revolution, and it is not necessary to 

 assume a more complicated shape. The mean radius of the earth 

 is determined to about 10(;» metres, which means a possibility of doubt 

 amounting to about one part in 60,000. 



Geodetic work is, however, not confined to measurements of length, 

 for important information may be derived from an exact knowledge 

 of the acceleration of gravity over its surface. The introduction of 

 the pendulum of short length intended for relative and not for abso- 

 lute measurement has greatly facilitated this work, and it is hoped 

 that these pendulum observations may be carried out over still more 

 extended regions. India is setting a good example. It has measured 

 two arcs of meridian, and the gravitational work carried out by 

 Captain Burrard, and recently published by the Royal Society, is of 

 primary importance. But, otherwise, British Colonies require en- 

 couragement to do more. I am assured that measurements of the 

 gravitational constant in Canada would be of the greatest importance. 



The bearing of such work on our knowledge of the earth may 

 perhaps be illustrated by one example. It has often been a matter of 

 wonder how mountain chains such as the Himalayas could rest on the 

 lower strata of the earth without crushing them and forcing them in 

 by the pure power of their weight, and the most plausible theory to 

 account for this \\'as found in the idea first suggested by Pratt that 



