502 INTERNATIONAL SCIENCE. 



east of Greenwich, and a large portion of it passes through Africa. 

 Owing to the great energy and enterprise of Sir David Gill, the work 

 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 betAveen representatives 

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

 in Berlin in 1896 Germany undertook to carry out the triangula- 

 tion through her territory in southwest Africa. I 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 Ehoclesia, but there is every hope that this will soon 

 be bridged over. The British South African Company have spent 

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

 portant enterprise. A^Tien the African arc is complete it wdll be con- 

 nected with the Russian and Roumanian arcs, so as to form a con- 

 tinuous 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 African arc is not the only 

 undertaking to which this country is called upon to pay attention. 

 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 present meas- 

 urements allow us to judge, the surface of the ocean can be well rep- 

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

 a more complicated shape. The mean radius of the earth is deter- 

 mined to about 100 meters, which means a possibility of doubt 

 amounting to about one joart 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 hoj^ed 

 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 per- 

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



