VOL. LXVII.] PHILOSOPHICAL TKANSACTIONS. 181 



Mr. de L. was surprised to have come so near to the geometrical measures, as 

 he had imagined, that the exhalations of all kinds in the mines must in some 

 measure aftect the common laws of the air's elasticity in different degrees of heat, 

 if not its absolute elasticity. On reflecting however on this singular conformity 

 of the air in mines with the external air, he soon found the cause of it in the 

 extreme care taken to procure a circulation of external air in the mines, in order 

 to prevent the pernicious effects of the exhalations; so that the same means, 

 which really preserve the health of the miners in their subterraneous abodes, 

 seem to give the air which circulates in them, and more especially that of the 

 pits in which are the principal currents, the properties of the external air as to 

 barometrical measurements. Doubtless this is the cause of that intei-esting phe- 

 nomenon, as satisfactory for the security it gives to the lives of the miners, as 

 for the application of the laws of aerometry: this was again confirmed by obser- 

 vations Mr. deL. made some days after in other mines, where indeed he met with 

 some irregularities, but not such as might have been expected from barely con- 

 sidering the local circumstances. 



These mines are in the Ramelsberg near Goslar. The ore that is chiefly ex- 

 tracted from them, as well as from those of Clausthal, is lead; but they are 

 worked in another manner. The vein of ore, which is near 1 8 toises broad, is 

 extremely impregnated with pyrites: insomuch that, when it is heated, the va- 

 pour of the sulphur, which disengages itself, bursts the stone, which falls down 

 in large fragments. The method therefore is to light great fires against the 

 rock; and, when they are extinguished, the miners assist with their instruments 

 the fall of the stones, that may still remain suspended. The following are the 

 results of his observations taken there, viz. 



The height of the gallery of Breitling, above the bottom of die pit of Kaunkuhl, 44-.4 1 French 

 toises; the height of the entr>' of the mines, above tlie gallery of Braiding, 27.04-; the height of 

 the top of the pit of Kaunkiilil, above the entry of the mines, by external observations, 41.27; 

 therefore the depth of the pit of Kaunkuhl, measured in 3 parts, one of them without die mines, 

 112.7C; and the depth of the same pit, determined by immediate observadons made at die top and 

 the bottom, 1 13.13 ; agreeing within a toise of the geometrical measurement. 



Having made these experiments within the mines, Mr. de L. was desirous of 

 making some in tlie open air, which he had soon a very agreeable opportunity of 

 doing; for the principal of the subterraneous geometers having had occasion to 

 determine most accurately the height of 2 external points of the Hartz, relatively 

 to the mines of Clausthal and Zellerfeld; nothing more was required but to ob- 

 serve the barometer at the entry of a certain mine, which was a fixed point, and 

 to observe it again at these 2 external points; one of which was about 3000 

 toises horizontal distance, beyond a small hill; and the other 5000 toises off^ 

 entirely without the Hartz. On carrying this project into execution, Mr. de L. 

 found the following heights by his calculations, viz. 



