VOL. LVl.] PHILOSOPHICAL TRANSACTIONS. 343 



grass downs. The tops of others are fields of wheat, which, in the year 1759, 

 gave a produce of 8 for one. All these vegetables grow in a soil, a foot or two 

 deep, which covers a rock, full of the most arsenical, sulphureous, silver, copper, 

 lead, and cobalt ores, in Europe, and most of the veins are near the surface. 

 The mines of Freyberg are in low hills near the city. He saw them all covered 

 with barley in July. A stranger would not imagine that men were reaping corn 

 over hundreds of miner's heads, who were blowing up veins of ore, arsenic, and 

 brimstone. The mines of Clausthal are in a plain, which, in truth, is the sum- 

 mit of a mountain ; the Dorothy and Caroline veins of silver, lead, and copper 

 ore, stretch away 8 miles to the Wild-Man mountain ; the finest meadows and 

 sweetest grass are on these veins, and all their branches near the city : they feed 

 900 cows, and 200 horses; they are mowed in June, and a second crop springs 

 up, which is mowed in August; a multitude of plants grow in these high mea- 

 dows, over the mines. 



It is true, he saw mines in the barren naked mountains and hills; but it is 

 certain that their barrenness is not the effect of mineral vapours; but the air, 

 moisture, heat, and cold, have more power over the surfaces of some rocks, 

 than of others, to moulder the stone into earth. Such is the high mountain of 

 Ramelsberg, above Goslar, whose inhabitants have lived by the mines found 

 there. Mr. B. crept up this steep rock to its summit; he found it split and 

 cracked into millions of fissures, from 1 foot to an inch wide; in other places it 

 was shivered into small rotten stones, which became a receptacle for a few plants, 

 grass, moss, &c. and, as this decayed stone moulders into earth, it will be more 

 abundant in vegetable productions: this may perhaps have been the original state 

 of those mountains, which are now covered with verdure. 



XXVI 11. On the Electrical Nature of the Tourmalin. By Torbern Bergman, 

 F. R. S., i^c. From the Latin, p. 236. " 



Mr. B. first describes several tourmalins in the possession of the r. s. of 

 Stockholm, on which he made experiments. They are very various both as to 

 shape and colour ; and are brought from different countries, as Ceylon, Brasil, 

 &c. As to the electric nature of the stone, he states it as a fundamental law, 

 that of any tourmalin, the one pole by dilatation acquires a positive electricity, 

 and by contraction a negative one; but that the other has a contrary nature, so 

 as by contraction to be made positive, and by dilatation negative. By a state of 

 contraction, the author means that in which the capacities of the pores are dimi- 

 nished, and a state of dilatation, when they are enlarged. Hence he determines 

 various particular cases of its states of positive and negative electricity. 



