106 Mr. F. A. Ahel [April 28, 



20 feet. Xo doubt a powerful air current in a mine, passing in the 

 direction in whicli the shot is fired, must hare a tendency to aid the 

 spread of the flame to a greater distance; but the difference between 

 20 feet and 100 feet, the flame having in the latter instance extended 

 to a distance of 75 feet along a gallery at right angles to the point of 

 ignition, is far too great to be only ascribable to the effect of an air 

 current in elongating the flame. As the first of the loopholes above 

 referred to existing in the walls of the gallery was 18 feet from the 

 shot, thev could hardly affect the distance to which the flame was 

 found to reach.* It will be observed that these results correspond 

 with those which 3JJr. Hall obtained with 4 lb. charges of powder in 

 an adit, the dimensions of which are not specified. 



Xo ^llerv of large dimensions and free from the small lateral 

 openings was available for the continuance of these experiments, but 

 it was thought that some experiments in subterraneous passages of 

 much smaller dimensions (military countermines) might give instruc- 

 tive results. A so-called eovelope gallery was therefore first selected 

 for the purpose. This gallery was 5 feet 9 inches high to the crown of 

 the arch, and 4 feet 9 inches to the springing of the arch, and only 

 2 feet wide. The part selected for the position of the gun and the 

 target was straight, but the portion immediately beyond was curved. 

 In rear of the gun, the gallery was quite open to a considerable distance. 

 One-and-a-half pound charges, untamped, were fired, and a frame- 

 target the width of the gallery and 4 feet 6 inches high, constructed 

 so as to give 15 points for the attachment of guncotton tufts, was 

 placed at gradually decreasing distances from the gun, commencing at 

 20 feet. Even at a distance of only 14 feet from the charge, none of 

 the guncotton tufts were inflamed : but the tarcjet was blown forward 

 about 12 feet and partly broken. It was evident that the faet of the 

 gallery being open at the rear of the charge greatly reduced the 

 tendency to the projection of flame to a distance in the direction of 

 the explosion. The resistance opposed to the movement of the air by 

 the curvature of this very narrow prallerv, a short distance in front of 

 the seat of the experiments, may have also contributed to diminish the 

 distance to which the flame or highly heated gases would extend. 

 When the experiments were continued in another gallery, of the same 

 dimensions, but straight and terminating in a head, like a drift in a 

 mine, the cannon being placed close up to the face of the drift, several 

 of the tufts of guncotton were inflamed at a distance of 27 feet ; one 

 was inflamed when the target was 30 feet off, and one also at a distance 

 of 32 feet, but none were ignited at a distance of 35 feet from the 

 charges. Here then, in a long gallery, narrow in proportion to its 

 height, but in all respects representing a drift way in a mine, the 

 distanc-e to which the flame of a blown-out shot of 1^ lb. of powder 

 extended was less than 35 feet, and therefore considerably less than 

 one-half the distance from the seat of the blown-out shot of 1 lb. of 



• The clc»=iDg up of these was not found to affect the resultij. 



