1 3 Biographical Memoir of M. Duhamel. 



look as if they had been subsequently filled with the foreign 

 materials at the bases of the mountain, and it is in the intervals 

 of these foreign rocks, in these veins, that the precious mole- 

 cules, often of very varied composition, are deposited. From 

 them the successive discoveries of chemistry have enabled us to 

 extract the metals in their pure state. 



The art of the miner consists in discovering principal veins, 

 in following them, in finding them again when they are inter- 

 rupted, in allowing none of the accessory veins which may in- 

 tersect them to escape ; lastly, in raising all the parts that may 

 contain metal, and in raising none else. He must therefore 

 know the general laws of the distribution of veins, of their in- 

 flections and intersections ; and when he has wrought out a 

 part, when he has perforated the mountain in every direction 

 in which veins have presented themselves to him ; when he has 

 scooped out a second time this labyrinth, which seems to have 

 existed since the original disruption of the rocks, and before the 

 substances which fill up the fissures were deposited ; he must be 

 able at all times to find his way through those gloomy recesses, 

 he must even retain an accurate knowledge of the galleries, of 

 the veins which he has abandoned, that he may not be annoyed 

 by the waters, on coming imprudently upon them again by a 

 different route. 



Such is the object of subterranean geometry ; it finds out the 

 direction of the veins toward the cardinal points, and their in- 

 clination to the horizon ; it fixes the three dimensions of the 

 works ; it follows them, and verifies their progress by clear and 

 distinct images. Its means are such as they might be in those 

 narrow cavities, where the view extends only a few feet, and 

 where the light of day does not penetrate. Some lamps, a 

 compass, and an instrument to measure the inclination, are all 

 that can be used. It cannot, like common geodesy, either con- 

 nect its operations with those of astronomy, or establish great 

 triangles, to rectify its small errors. It therefore requires par- 

 ticular methods, which supply by their accuracy of detail those 

 grand means of rectification ; and these methods must be such 

 as men of the class who pass their melancholy lives in those 

 depths, may comprehend and execute with sufficient accuracy. 



These operations are what M. Duhamel teaches in his book. 



