446 Mr. W. Galloway on Safety -Lamps. [June 18, 



cylinder of cotton-wool was one inch further from the origin of disturb- 

 ance. 



Two sets of apparatus (figs. 1 & 2, Plate VI.) were now constructed : 

 in both the sound-wave of a pistol-shot is conveyed through tin-plate 

 tubes to a distance of 20 feet; then it passes through a safety-lamp, 

 which can be surrounded by an explosive mixture of gas and air. 



In the apparatus represented in fig. 1 there are two tubes, each 10 feet 

 long by 3 inches in diameter. At the end o a disk of wood, | in. thick, 

 with a hole in the centre large enough to receive the muzzle of the pistol, is 

 fitted into the tube a ; at c a sheet of india-rubber, -fa in. thick, is tied 

 over the end of the tube b, and a tubular ring, one end of which is 

 covered with a network of wire T ^ in. thick, with meshes -f-% in. square, 

 is drawn over the fastening till the network is close to the diaphragm. 

 The part of the apparatus which is surmounted by the safety-lamp is of 

 the following construction : A round sheet-iron plate, g, of 6 in. dia- 

 meter, rests on four short legs : above this, and joined to it, is a circular 

 chamber, /, formed of two concentric tubular rings and two flat rings ; 

 its exterior diameter is 2| in., its interior diameter is 1| in., and in the 

 top ring there are twenty-four small equidistant holes, whose locus is a 

 circle of 2 in. diameter. The screw which receives the lower ring of the 

 wire gauze is carried upon projections inwards from the upper flat ring 

 of the chamber /. The wire gauze of an ordinary Davy lamp, held 

 between two rings in the usual manner, incloses a space in which a small 

 gas-jet occupies the position of the wick in the oil-lamp, when screwed 

 into its place above the chamber /: the three stout wires joining the 

 upper and lower rings are omitted in the figure. A rod, I, screwed into 

 the plate g, carries a short narrow plate at its top, bent to the curve of 

 the tube b which rests on it ; there is a strip of iron fastened to the tube, 

 on each side of this support, to prevent it from altering its position 

 relatively to the lamp. The part of the tube b opposite to the wire 

 gauze is cut out, so as to leave a clear space of half an inch all round for 

 the passage of the explosive mixture. The pipe Ji conveys gas to the 

 chamber /, and the pipe k supplies the jet in the inside of the wire gauze ; 

 the quantity is regulated by screw-clips on the india-rubber tubes. 



The experiment is made in the following way : A pistol, of which the 

 barrel is J in. bore and 5 in. long, is loaded with -205 gramme of gun- 

 powder, and several pieces of paper are rammed down well upon the 

 charge ; the firing is done by a cap. The gas-jet of the lamp having been 

 lighted and the wire gauze screwed into its place, gas is made to pass 

 into the chamber /, and escaping by the holes in the top, it mix.es with 

 the air and forms an explosive mixture, which surrounds the lamp : part 

 of the explosive mixture passes into the interior, where it is ignited ; the 

 remainder passes up on the outside. The muzzle of the pistol is then 

 placed in the hole in the wooden disk, and as soon as the shot is fired 

 along the axis of the tube, a large flame leaps up, and continues to burn 



