Lance-Corporal Jarvis preparing to destroy a Bridge.
Drawn by Ernest Prater from a rough sketch by Lance-Corporal Jarvis.
Engineers destroy a bridge such as the above by fixing one or more slabs of gun-cotton in close contact with it. Wires are attached to the gun-cotton, and by means of electricity the charge is fired. The engineers must calculate the amount of gun-cotton required, and choose the most suitable position for fixing the charge, so that the explosion may have the desired effect.