Page:Popular Science Monthly Volume 9.djvu/39

Rh those which are by many still considered to produce the most perfect of hammered work, the "wiper" was so shaped as to throw the hammer very high. The ascent was checked by a powerful spring, and thus the ascensional energy was reversed and added to the accelerating force of gravity downward; and so not only was the intensity of the blows increased, but their frequency also. This spring took the place of that muscular energy which brought the hammer down with intensified effect.

Hence, also, in steam-hammers, all muscular effect to intensify the blow is transferred to the steam, and all consequences of centrifugal action, whether from hand or tilt hammers at the ends of arms, are removed. Further, in steam-hammers nowadays, the steam operates to check as well as to intensify the blow. This checking action is called "cushioning," and it seems to do what an elastic handle does in a sledge-hammer: it relieves the rigid fabric or erection from jar or destruction. "Cushioning" is brought into play by admitting steam for the purpose of checking the intensity of the blow due to the action of gravity alone, or of steam combining with gravity upon the hammer. Hence the perfect control over large steam or air worked hammers, and the rapidity with which the intensity of the blow may be changed. Such control as this over a sledge-hammer is beyond our bodily powers. We may intensify the blow, but we cannot, except just experimentally, and for the purpose of display, bring the restraining power of the muscles to diminish the energy of the descending hammer.—Journal of the Society of Arts.



R. CARPENTER is master of the domain which he has appropriated for the last age, that of physiology. He has done more than any living man, not exactly to advance, but to combine and expound, the discovered truths of his science. But he is ever impelled by his intellectual sharpness and his cultivated tastes to take excursions into other regions, and I am not sure whether he has there been so successful. In particular, as dwelling so near the territory of mind, he has ever been crossing into it. He has made a very careful survey of the border-country, and given us the result in his valuable work "Mental Physiology." Ever since the palmy days of mesmerism and 