Although annealed glass will break with the greatest facility by unequal pressure (or vibration of the particles from a centre), yet it is found to withstand uniform or equable internal pressure greater than either of the metals.

The property of welding by contact at about a red heat is peculiar to Glass, whether with or without lead. But for this useful fact in the ornamental department of Flint Glass, as regards the addition of handles, feet, rings, &c., the manufacturer would be left without those manipulatory decorations of his art. So perfect are the weldings, that at the points of union they become as completely one homogeneous mass as if the whole were gathered in one piece; yet, the slightest sulphurous or carbonaceous film intervening between the parts required to be welded, will cause the cohesion utterly to fail.

Another peculiarity, of which the manufacturer avails himself, is the liability of Glass to fracture instantaneously by contact with a cold metal, or by any sudden chill; this causes instant contraction of the part affected, which cracks through the mass by a slight blow, as perfectly as if cut with a diamond. Welding by contact, and separation by contraction, are therefore two principles, without which the manipulations of the Glass-blower would be comparatively inoperative.

Having disposed of a few of the peculiarities and eccentricities of Glass, we proceed to give some account of its manipulatory conditions. One of these depends upon a constant rotary motion being given by the workmen to the Glass gathered upon a hollow blowing-iron, which will, when done with judgment, not only prevent the Glass from falling from its position, but if rapidly rotated, will increase its diameter on the principle of centrifugal force. If a depressed form