358 



A Portable Telemeter, or Range-finder. 



[Feb. 22 r 



Separate Mean 

 results. observed. 



Actual 

 distance. 



Computed- 

 observed. 



Mowbray Church 



Cement Works Chimney, 

 Salt River 



Salt River Works Chimney. . 



ET.E. corner of cottages 

 between Observatory and 

 Salt River 



Chimney of Oude Moilen. . . 



Spire at Altentby Asylum . . 



Spire at Clarendon Mow- 

 bray 



Chimney at Nieuve Moelem 



1860 

 1885 

 1825 

 1430 

 1410 

 1405 

 1715 

 1735 

 1705 

 861 

 858 

 850 

 701 

 702 

 711 

 751 

 744 

 733 

 1910 

 1950 

 2050 

 1350 

 1395 

 1380 



f 861 I 



{ 858 y 



L 850 J 



r 751 1 



I 744 [ 

 { 733 J 



2 1 



J 



yards 

 1857 



1415 



1718 



856 



705 



743 



1970 



1375 



yards. 

 1859 



1432 



1711 



852 

 686 

 749 

 1994 

 1388 



+ 2 

 + 17 

 -7 

 -4 

 -19 

 + 6 

 + 24 

 + 13 



[Since the above was written, the instrument has been carried on 

 horseback between 300 and 400 miles in less than three weeks with 

 Colonel Crabbe's column in the South African War. The author- 

 frequently tested with the collimator the parallelism of the prisms in 

 each half of the base. The error never amounted to 1 minute of arc. 

 Applying this in the formulae of the paper, it follows that the angle cc 

 may amount to 1° without introducing an error of 2 J", the limit of 

 accuracy aimed at. In other words, while it is shown in the paper 

 that the error increases with the vertical angular distance of the object 

 aimed at from the centre of the field, the tests during a rough 

 experience show that the limit of accuracy aimed at is not exceeded, 

 though the object be in any part of the field of view, and that no 

 adjustment is required after leaving the maker's hands.] 



