Spring weighing scales have recently been invented, which will accurately and automatically show not only the weight but the total price of the goods weighed, the price per unit being known and fixed. In the weighing of large masses of coarse material, such as grain, coal, cotton seed, and the like, machines have been constructed which automatically weigh such materials and at the same time register the weight. Previous to this century no method was known, except the exercise of good judgment in the light of experience, of accurately testing the strength of materials. Wood and metals were used in unnecessarily cumbrous forms for the purpose to which they were put, in order to ensure safety, or else the strength of the parts failed where it was most needed. The idea of testing the tensile, transverse, and cubical resisting strength of materials has been applied to many other objects than beams and bars of wood and metals; to belts, cloths, cables, wires, fibres, paper, twine, yarn, cement, and to liquids. Kiraldy, Kennedy, and others of England, Thomasset of France, Riehle of Germany, and Fairbanks, Thurston and Emery of the United States, are among the noted inventors of such machines. In the Emery system of machines, consisting of scales, gages, and dynamometers, the power exerted on the material tested is transmitted from the load to an indicating device by means of liquid acting on diaphragms. The same principle is employed in his weighing machines. By one of these hydraulic testing machines the tensile strength of forged links has been ascertained by the exertion of a power amounting to over 700,000 pounds before breaking a link, the chain breaking with a loud report. The most delicate materials are tested by the same machine--the tensile strength of a horsehair, some of which are found to stand the strain of one and two pounds. Eggs and nuts are cracked without being crushed, and the power exerted and the strain endured automatically recorded. Steel beams and rods have been subjected to a strain of a million pounds before breaking. Governments, municipalities, and the people generally are thus provided with means by which they can proceed with the greatest confidence in the safe and economical construction and completion of their buildings and public works. CHAPTER XXVI. MUSIC, ACOUSTICS, OPTICS, FINE ARTS.