the Depth of the Mines in the Hartz. 423 
A twilled brafs wire five toifes long, two puncheons, 
a femi-circle, and a compafs, are all the inftruments made 
rife of by the fubterraneous Geometer.. By means of his 
two puncheons, he extends his wire in the direction of the 
way which he is meafuring : and by practice he acquires 
a habit of always llretching it to the fame degree. His fe- 
mi-cirele, which is very light, being fufpended at the mid- 
dle of the wire, fhews him its inclination. By this means 
he has a right-angled triangle, of which the hypothenufe 
and angle at the bafe are known. He has confequently 
the vertical height and horizontal diftance gone over. 
After this he fufpends his compafs to the wire, in order 
to find out its declination, and confequently the direction 
of his horizontal line. It is in this manner that, he draws 
the plan and fedlion of thefe fubterraneous labyrinths. It 
is likewife by this means that he goes over hills and vales, 
in;. 
Un fil de leton tordu de 5 toifes, deux poin£ons,un demi-cercle, et vine boufible, 
font tous les inftrumens du Geometre fouterrain. II etend fon fil, par ]e moyen 
de fes deux poin^ons, dans la dire&ion du trajet qu’il mefure; l’habitude le lui 
fait tendre toujours au merne degre. Son demi-cercle, qui eft fort leger, etant 
fufpendu au milieu de ce fil, lui en montre I’inclinaifon; il a par ce moyen un 
triangle re&angle, dont l’hypothenufe et d’angle fur la bafe iui font connus : 
il a done la hauteur verticale et la diftance horizontale parcourues. . II fufpend 
enfuite .fa bouffole au meme fil, pour en connoitre la declinaifon, et par confe- 
quent la dire£lion de fa ligne horizontale. C’eft ainft qu’il tire le plan et la 
coupe de ces labyrinthes fouterrains : et c’eft ainft encore qu’il va chercher au 
3 dehors • 
