Annual Address to the Members. Ixvii 



One of the duties that appeared to be laid upon me by the tradi- 

 tions of the Observatory and tlie labours of my predecessors was 

 that of the geodetic survey of the Colony. Lacaille in 1752 had 

 measured an arc of meridian at the Cape, and his results appeared 

 to prove that the form of the earth v^as different in the southern 

 from the northern hemisphere. It was a matter of very great 

 scientific importance to decide whether this discrepancy arose from 

 any errors in Lacaille' s work, or was due to non-symmetry in the 

 form of the earth. 



Fallows, during the period of his enforced idleness, or rather, 

 when he had only insignificant instruments at his disposal, pressed 

 the desirability of employing his time in this work, but the request 

 was unwisely refused. It was to settle this question that Maclear 

 undertook his revision and extension of Lacaille 's arc. He found a 

 small error in the astronomical length of Lacaille's arc, due to local 

 attraction at the Southern Station, and two unavoidable errors in the 

 triangulation produced by the comparatively crude instruments and 

 methods of the day. He extended the arc nearly to the northern 

 limits of the Colony, and southwards to Cape Point, and it was the 

 great triumph of Maclear' s life's work to prove that the form of 

 the earth, so far as it was possible to derive such a result from a 

 comparatively small arc of meridian, was symmetrical in the 

 southern hemisphere with that of its known form in the northern 

 hemisphere. 



Besides settling this scientific question, Maclear's work was of 

 immense value to the Colony in rigorously determining the position 

 of important points which served as the groundwork of the future 

 survey of the Colony. Prominent points visible from the sea were 

 in some instances marked twelve miles in error on the best maps 

 previous to the surveys of Maclear and Bailey. It became, then, one 

 of my first objects to urge upon the Colonial Government of the day 

 the extension of the geodetic survey of South Africa. I submitted a 

 plan, and recommended the employment of officers and men of the 

 Eoyal Engineers for the work. The proposal was strongly supported 

 by Sir Bartle Prere, by Sir George Colley, and Sir Charles Mitchell, 

 and finally an agreement was arranged between the Government of 

 Natal and the Cape Colony to carry out the work jointly on the plan 

 which I had proposed. 



Time does not permit me to go into the details of this work — I 

 find it necessary to reserve this for a separate occasion. Suffice it 

 for the present to say that between the years 1883 and 1894 the 

 complete principal triangulation of the Cape Colony and Natal was 

 carried out by Colonel Morris, and I had the satisfaction of com- 



