in the Coed-Mines of Germany. 379 



by the authorities in the fullest manner, having received in- 

 formation from many officers of the coal-mines relative to the 

 subject, and having had access to all public papers regarding 

 the use of the safety-lamp, in Prussian coal-mines, during the 

 last twenty-one years, I was enabled to become acquainted 

 with this subject, and the experiments made in these mines 

 about it. 



Notwithstanding that the safety-lamp has been used in the 

 Prussian coal-mines during this space of time, even in the 

 most dangerous localities and under the most trying circum- 

 stances, yet not a single accident has occurred fatal to its 

 security. But I have frequently heard complaints as to its 

 small illuminating power. I had therefore **great many 

 safety-lamps made, whose cages of wire-gauze had apertures 

 of different sizes. 



Experiments regarding the security of safety-lamps are 

 rather difficult. By placing the lamps in a locality filled with 

 an explosive mixture, sufficient results are obtained, provided 

 the place be very large, or if new quantities of the explosive 

 mixture are constantly passing through it. On the contrary, 

 when the quantity of the explosive mixture is too much li- 

 mited, the intenseness of the burning of the explosive mixture 

 within the cage gradually decreases, and the wire-gauze pre- 

 vents the passage of the flame through it, from not having 

 reached the red heat, Indeed, a lamp may only be consider- 

 ed as conferring safety, when no communication of explosion 

 takes place when the wire-gauze is perfectly red hot. 



Considering these circumstances, it is obvious, that it is 

 only by placing a lamp near the spot where a quantity of in- 

 flammable gas is issuing and mixing with the circulating cur- 

 rent of atmospheric air to the explosive point, or by con- 

 veying a lamp into a very large space filled with an explosive 

 mixture, that its safety can be proved. 



In order to institute experiments according to the former 

 method, I caused to be made a cylinder of pasteboard 24 

 inches in height and 15 inches in diameter. The cylinder 

 was furnished with four small glass windows for observing 

 the phenomena taking place in its interior. The cylinder was 

 closed by a cover and a bottom. The former had five holes, 



