DESCRIPTION OF THE SUBTERRANEOUS GRAPHOMETER. gg5 



XI. 



Description of the Subterraneous Graphometer invented by M. 

 Komarzewski, F. R. S. and prefented to the National Injli- 

 Jiitute of France *. 



A HIS inftrument is a fimple conftru&ion of the common Defcription of; 

 theodilite, and is calculated to anfwer the author's intention 1^1™"^* 

 in operations like thofe of mining, where great accuracy is not 

 required. 



The rougheft kind of furveys are made by taking angles 

 with the compafs,, and thefe are itill ufed in mines, and in the 

 diftricls of unfettled countries. Our author has taken the next 

 procefs, and obtains confiderably more accuracy, without de- 

 viating from fimplicity and cheapnefs. 



This fubterraneous graphometer is compofed of three prin- 

 cipal parts, viz* a circular horizontal plate, a circular vertical 

 plate, and a pedeftal, which are refpeclively reprefented in 

 perfpedive, (Figs. 2, 3 and 5, Plate XV.) 



The horizontal Plate A. Fig. 2. is divided into 360° doubly- 

 numbered, the fubdivifions are carried to 15', this is confidered 

 fufficient for mines where there is feldom light enough to ob- 

 ferve a more minute divifion : for operations on the furface of 

 the earth a Vernier's fcale may be added. 



Within the line of divifions above mentioned, is that of the 

 magnetic compafs : which gives the reduction of hours into 

 degrees, and that of degrees into hours. 



This plate meafures the horizontal angles which the miners 

 call the direction. 



Through its centre pafles the cylinder a, on which turns the 

 hollow cylinder, which forms the centre of the horizontal index 

 bb, and carries the vertical plate B, as reprefented in Fig. 1. 



The horizontal index is one inch in breadth, and is increafed 

 at the centre by two circular fegments cc call with it, in 

 order to give the vertical plate a more firm bearing on the 

 horizontal plate at the top of the cylinder a, a fcrew a is in- 

 ferted to confine the cylinder. 



* From a folio publication in Engli/h, entitled, Memoir on a 

 Subterraneous Graphometer, &c. published at Paris by Pougens, 

 1803. 



The 



