latitude and longitude of campos rodrigues. 39i 



(Translation.) 



DETERMINATION OF THE LATITUDE AND LONGI- 

 TUDE OF THE PILLAR OF THE TRANSIT 

 INSTRUMENT AT THE CAMPOS RODRIGUES, 

 OBSERVATORY. 



By AuGUSTO DE Almeida Teixeira. 



No new matter is dealt with in this paper, and I am intro- 

 ducing it only on the plea of the interest attaching to the know- 

 ledge of the agreement existing between the results obtained from 

 the geodetic observations connected with the triangulation of the 

 Transvaal and those obtained from astronomical observations. 



The most valuable part of this work is not due to myself, 

 but to Commander Gago Coutinho, of the Portuguese Navy, 

 head of the mission that undertook the geodetic survey of the 

 Districts of Lourengo Marques and Inhambane. This officer is 

 at present engaged in a new mission delimiting the Barotse 

 frontier, and as it would not, for that reason, be an easy matter 

 to consult him, I have been compelled to avail myself of one of 

 his works published two years ago, from which I transcribe the 

 following paragraphs on the determination of the co-ordinates of 

 the pillar of the transit instrument : — 



" Seeing that it was impossible to include this pillar in the 

 main triangulation, as none of the points of this triangulation 

 could be sighted, and that its distance from the geodetic station 

 of the Observatory, which is installed in the tower of the 

 meteorological instruments, could not be measured direct, it 

 became necessary to resort to an indirect method, by measuring 

 with precision a small base of 48 metres on the ground, and join- 

 ing this high station with the pillar by m.eans of a triangulation 

 with five points, thus forming two quadrilaterals. The precision 

 of the measurements and the closing of the triangles made it 

 possible to determine the distance between the geodetic and 

 astronomical stations with a probable error of less than one 

 millimetre, which was more ^ than sufficient for the purpose, 

 seeing that each thousandth of a second is equivalent to about 30 

 millimetres. The following differences between the two stations 

 resulted from this work : 



Latitude — i '.495 



Longitude -f- i"-647 



This station was connected with the beacon of the frontier of 

 Swazieland, at Ipoy, the co-ordinates of which are determined 

 by the triangulation of the Transvaal, to which this vertex also 

 belongs, and this connection was carried out through the network 

 of the main triangulation of the geodetic mission which joins the 

 geodetic station of the Observatory with the frontier, and which 

 comprises 17 vertices. 



