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XIY. 



A CIECUMFEEENTOE. 



By SIE HOWAED GEUBB, F.E.S., Vice-President, Eoyal Dublin 



Society. 



(Plate XI.) 



[Bead, November 17 ; Eeceived for Publication, November 20, 1903 ; 

 Published, February 10, 1904.] 



The instrument of which the accompanying figure shows a vertical 

 section is primarily intended for rapidly observing horizontal and 

 vertical angles for military purposes ; but it is expected, that it 

 will also prove of use for many other purposes, notably for 

 underground survey work, mines, &c. 



Its construction is exceedingly simple. A circular box, b, b, 

 is provided on the inside of its rim with a transparent circular 

 scale, s, divided into tenths of degrees. 



The lid, /, /, or upper portion of the box, is so constructed that 

 when in use it revolves freely upon the lower. 



This lid carries on its under side a pair of plano-convex lenses, 

 with the convex faces towards one another, the combined focus of 



