DESCRIPTION OF THE SUBTERRANEOUS GRAPHOMETER. 285 



ftaples//foldered to the horizontal plate A, which enter two Defcription of a 



fubterraneoui 

 graphometer. 



correfponding holes in the plate D, and are confined by the fubterrai 



bolts //Aiding in grooves foldered beneath the fame plate. 



In the centre of the plate D as well as in the centre of the 

 inferior part of the ball K, is a female fcrew i t to receive 

 the folid cylinder L, Fig. 4, the ufe of which will be feen in 

 the folution of the problems. This cylinder is furnifhed with 

 a moveable collar m, having a hook in its centre, to which the 

 other extremity of the cord may be attached. 



Fig. 1 . is a perfpettive view of the graphometer, in which 

 A is the horizontal plate, B the vertical plate, a a the centre 

 of the vertical plate, &c. b b the horizontal index, d d the 

 vertical indexes. 



From this difpofition it refults that, when one direction is 

 known, which for the firft operation may be determined by 

 the magnetic compafs, or in mining ftill better by a meridian 

 line pafling through one of the principal (hafts, the inftrument 

 may with facility be directed to any given point, and all plans 

 be executed which are neceflary in operations of mining, with- 

 out making ufe of the magnetic needle, and that the direc- 

 tions and inclinations may be taken at the fame time, fince in 

 all thefe operations it is only neceflary to obferve the angles 

 indicated by the inftrument, to meafure the length of the line, 

 and to calculate right angled triangles, of which three parts 

 are known. 



The pedeltal is intended to be placed at the point of the 

 angle fought, and the cords flretched to it from the grapho- 

 meter, the cord is fixed to the hook of the graphometer by a 

 noofe, and its other extremity to the cylinder L of the pedeftal, 

 by means of the fcale and pin reprefented at Fig. 6. 



Experiments 



