98 ANNUAL OF SCIENTIFIC DISCOVERY. 







clear breach was made through both rows of timber, practicable 

 for an attacking party to get through. The effect was very much 

 superior to that of the 200 pounds of gunpowder. Immense 

 pieces of timber were hurled through the air to a great distance, 

 mostly in the rear of the stockade. Not so wide an extent of 

 timber appeared to be shaken as by the first explosion, but the 

 work was more completely done ; the results, indeed, were extraor- 

 dinary. Experiments were also made by exploding discs of 

 gun-cotton against single balks of timber, to show what effect 

 would be produced if timber bridges had to be destroyed. Four 

 balks of timber, about 16 inches square, were sunk in the ground 

 some feet apart, in a square, and braced together by thick pieces 

 of plank. A " necklace " of small discs of gun-cotton was formed 

 (about 68 in number) ; this was doubled and placed half round 

 one of the timbers. The explosion of this string of discs tore away 

 the wood for some depth, 4 inches or more on one side of the balk, 

 but did not break it, though the massive timber was much rent. 

 Three or four larger discs were then exploded on one side of the 

 timber, and tore out a large portion of the wood. A single " neck- 

 lace " of small discs, 65 in number, and weighing 2 pounds, was 

 then placed round another balk, quite encircling it. When ex- 

 ploded this tore out the wood all round to some depth. Then 12 

 of the larger discs, weighing 4 pounds 2 ounces, were hung on 

 nails on three sides of the timber, and exploded. The explosion was 

 very powerful, and the large balk was cut in two ; snapping off 

 where the gun-cotton had been attached, but falling on the side 

 where there had been no discs and partially splitting on that side. 

 The spectators cheered at this decisive proof of the value of gun- 

 cotton for this special purpose. All these experiments appeared 

 to be very satisfactory. At that part of the lines in front of St. 

 Mary's Barracks, a number of mines and galleries had been exca- 

 vated and charged with gunpowder or gun-cotton. One mine 

 had a charge of 500 pounds of gunpowder ; a second similar mine 

 was charged with 200 pounds of gun-cotton. Two smaller mines 

 were charged respectively with 21.6 pounds of gunpowder and 

 8.6 pounds of gun-cotton. These mines were successively ex- 

 ploded by means of an electric current. In the larger mines the 

 powder appeared to be the most effective agent. In the explo- 

 sion of the 200 pounds 1 charge of gun-cotton, a peculiar effect 

 was produced ; first, there was the eruption of brown clay and 

 smoke, and then a large flame, produced by the ignition of the 

 gaseous products of the explosion. The officers then proceeded 

 to the old Engineer Depot, near St. Mary's Convict prison, and 

 walls which are to be removed were experimented upon ; they are 

 18 inches thick ; charges of gun-cotton ranging from 2 pounds to 

 3 pounds were exploded against these walls, with satisfactory 

 results, making breaches in them. The officers then returned to 

 the scene of the mines, where two long galleries had been pre- 

 pared, one charged with 240 pounds of gunpowder, the other with 

 96 pounds of gun-cotton. These charges were exploded. The 

 object was to ascertain if it is practicable to form trenches in this 

 manner, instead of throwing them up while exposed to the en- 



