Page:Popular Science Monthly Volume 11.djvu/715

Rh not have been fully realized. The softer tissues still remained of wood of various kinds, and other such essential materials. With the acquisition of an iron frame or vertebra equal to the tensile strain of thirty tons without danger of fractures, came the temptation to employ strings of greater thickness, with a tension of from eleven to sixteen tons. These strings, stretched as near as possible to the limit of elasticity, that they might give forth the most vigorous vibrations, required to be set in motion by blows from hammers specially adapted for the purpose. (Voices similarly strained on the highest notes within their compass also have the most brilliant quality, as for instance the "G" of Mr. Santley and the chest "C" of Tamberlik.) Then, again, the increased powers of the instrument made greater demands on the sound-board.

If we compare the vibrations of the violin, set up by the comparatively gentle friction of the bow, with those of a piano-forte sound-board, violently trembling in response to strong percussive accents, and the multitudinous and continuous vibrations of long, thick metallic strings, it is at once evident that they are of a more extraordinary nature. Great discrimination was used in the selection of the wood from the spruce-trees of the Northern forests; many experiments were made to discover which way the grain of the wood should be disposed, and. in what manner the sound-board should be compelled to receive and transmit impressions without fear of such derangements as should lead to a state of paralysis. To make it act most energetically the fibres were permanently compressed longitudinally, as in a vise, up to a certain point, similar to the strings, which, as we have just now seen, give forth tones of most satisfactory quality when stretched to the verge of breaking. There is a readily-found precise limit to this compression, after which the tones become hard and thin in quality. The sound-board is now also slightly curved, forced upward or made convex that it may resist the downward pressure of the bridge that holds the strings slightly elevated from their level, to secure a complete and intimate communion for the transmission of vibrations. It is clear that, if, from any cause, a sound-board should become concave, or loose at any of the sides, serious consequences would ensue. Considerations such as these sufficiently prove that the attainment of a perfect harmony among the parts, to resist successfully external influences, was no slight undertaking.

The American piano-forte has, however, attained a constitution that will endure dryness, cold, and even furnace-heat, but succumbs to excessive dampness. A good instrument, dried to the utmost, rapidly absorbs moisture. The well-fitted parts, having no room to swell, then become rigidly bound together, and thus the action is destroyed. It would therefore suffer if placed in a room having no sub-cellar, under which water-courses might be formed after rains. An inferior instrument made with damp materials and kept damp by