284 DESCRIPTION OF THE SUBTERRANEOUS GRAFHOMETER. 



Defcriptionof a The hook attached to one extremity of the horizontal index 



fubterraneous is intended for the fufpenfion of a plumb line, 

 graphometer. . J* '„ ; r . 



The vertical plate B, Fig. 3, is only fix inches in diameter, 



in order that the extremities of the horizontal index may be 



left perfectly clear. 



Two indexes d d, are moveable round its centre c, which 

 meafure the angles of inclination. They are fomewhat nar- 

 rower than the horizontal index. Their extremities are like- 

 wife furnifhed with threads to mark the quantity of the angles 

 to the extremities of thefe indexes, and in the direction of their 

 axes are fixed two hooks in order to receive the cords which 

 put the indexes in motion. 



The vertical plate is divided on each fide by two lines paf- 

 fing through its centre, one of which is horizontal and the 

 other vertical, the one mark the diameter, and the other the 

 radius. The upper part of the plate is likewife divided on 

 each fide into twice 90. This divifion commences at the hori- 

 zontal diameter, and proceeds to the vertical radius, the lower 

 part which is but a fegment of the circle, contains only on each 

 fide 30°, this is fufficient for a lode or gallery in mines, more 

 confiderable inclinations being meafured like the depth of a 

 fhaft. 



Thefe two plates with their indexes form the graphometer, 

 the other parts belong to the pedeftal, on which it may be 

 moved as occafion requires. Its dimenfions depend upon the 

 v fpace in which the graphometer is to be employed. The pe- 

 deftal is represented at Fig. 5, as follows, 



A board EE about 18 inches long, fix inches wide, and one 

 in thicknefs, receives in a focket made its centre, the brafs ball 

 K, furmounted by the cylinder H cafi: with the ball, the board 

 is bored towards its extremities, to receive brafs fcrews, by 

 which it is fixed on fome wooden bar in the mines. 



The ball K is covered by a fquare plate g, which is concave 

 and perforated in its centre, and is fixed to the board E by the 

 four fcrews h: it is by loofening or tightening them that the 

 graphometer is fixed or levelled. 



On the cylinder H turns the hollow cylinder F, which is 

 caft with the fmall plate D, this hollow cylinder is furnithed 

 with a tightening fcrew G, to fix the graphometer when placed 

 upon the plate D : the graphometer is fixed to this plate by two 



ilaples 



