in (he Coal-Mines of Germany. 383 



lamp of 784 apertures to the square inch to burn in the appa- 

 ratus placed near the blower of Gerhard's gallery during 

 eight hours. After two hours the wire-gauze was covered 

 with soot, and after three hours the meshes were greatly 

 closed up. The flame was extinguished without an explosion 

 ensuing. After this, the wire-gauze was cleaned and the 

 lamp placed again in the apparatus ; the same phenomena 

 were now observed in a still shorter time. 



I shall not quote farther experiments instituted in places 

 40 inches in height and in diameter, in a coal-stratum where 

 exhalations of inflammable gas were to be supposed to exist, 

 but I shall give an account of experiments made on such 

 a large scale as to afford results of the most exact kind. 



I caused an excavation of 14 feet in height, 5 feet in length, 

 and 3 3 feet in breadth, to be made in a coal-stratum in the 

 vicinity of the blower of Gerhard's gallery. This excavation, 

 called in Germany, " Uebersich brechen, 1 ' being above the gal- 

 lery, experimenters standing in the latter, where there was 

 good ventilation, were enabled to make their experiments 

 without danger. The excavation was soon charged with fire- 

 damp. 



The lamps from No. 1 to No. 13 were in succession drawn 

 up into the excavation, and remained in it from five to ten 

 minutes, during which time they were strongly agitated. 

 Though the effects produced by the explosive mixtures were 

 very vehement, for the wire-gauzes became quite red-hot, the 

 whole cylinders were filled with fire, the oil began to boil, and 

 a humming noise like that of the chemical harmonica was 

 heard, yet the wire-gauzes remained quite impermeable to 

 flame. Some of these lamps, drawn up too high into the ex- 

 cavation, were extinguished. The lamp No. 3 fell down, as 

 the pack-thread by which it was suspended was burned, but an 

 explosion did not take place. No. 5 caused, it is true, an ex- 

 plosion, but it was found that the wire-gauze, from its hav- 

 ing remained for eight minutes in the explosive mixture, 

 had suffered oxidation, and had fallen to pieces. 



On the contrary, the lamp No. 14 instantly effected an ex- 

 plosion, before the wire-gauze became red-hot. It was there- 

 fore not necessary to employ the lamps after No. 14, as they 

 would doubtless have given the same results* 



