three of these, the texture of each being closer than that above it, so that large-grain powder is retained on the first, while fine-grain and dust fall through it. The fine-grain remains on the second, and the dust passes on to the third. All the screens are placed in an inclined position, so that the powder runs down them into tubs arranged at the lower end, one of which receives the large, another the fine-grain, and a third the dust.
The powder is then rolled for some hours in the glazing-barrels, to break off all minute irregularities, and give it a smooth surface. Then it is dried, and finally freed from dust in the slope-reel. This done, it is finished by being passed once more through the glazing-barrels, and it is then packed in barrels of 100 pounds each.
Such is the process of the gunpowder manufacture in the Royal Factory at Waltham. We have only briefly indicated the principles of each process, for to go into detail would occupy far greater space than is at our command; but even this sketch will show how at each step science has been called in to aid art in bringing the manufacture to its present high state of perfection. No expense is spared in procuring the best materials, the most efficient machines, and the most accurate tests; yet the cost of manufacture is only about seven-pence per pound. What a contrast to the early days of gunpowder-making, when in France, in 1375, a pound of gunpowder cost a sum equal to ten pounds of our money!
In every department the greatest care is taken to prevent the danger of explosions. The houses are built from 200 to 400 yards apart. Wood, copper, and gun-metal, are the only materials used in the structure of the machines, except where, and that rarely, a bolt of iron is introduced for the sake of strength, and then the metal is encased in leather. The floors are covered with hides secured with copper nails, and these, as well as the wooden platforms round the houses, are kept constantly wet. All loose powder is swept away from the floors, damped, and carried to a magazine, where it is collected and the saltpetre subsequently extracted. No one is allowed to enter a room without putting on a pair of leather "magazine shoes" made without nails, as the iron nails in ordinary boots might lead to an explosion if one trod on the loose powder; and, moreover, one would be certain to bring in grains of grit, which are so dangerous if they become mixed with the powder. The men wear a kind of fire-proof clothing, and in the incorporating-houses leather caps and gloves. Fire-engines are stationed in various parts of the factory, and every man has his post assigned to him in the event of an alarm of fire. To such an extent are these precautions carried that the roofs and eaves of the buildings are searched for birds' nests, and they are pulled down whenever they are found, lest the birds, in building or bringing food to the young, might drop grains of grit or sand on the platforms round the houses. Every building is protected by lightning-conductors, and, as soon as a thun-
