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Let Fig. i represent the new apparatus and Fig. 2 the old. We will first consider its application as a lever. Traction is exerted on the ends of the spine, at a and c, pressure applied to the point of curvature, at b. As in each instance b is the fulcrum of the lever, the pressure at that point will equal the sum of the forces applied at a and c, therefore, as levers, we see that the two appliances are identical. As springs, they differ materially. In Fig. 1 the spring is a, c, b, which isdoi:10.1001/jama.1885.02390820008002 fatcat:voswyvpy2fectjogr2lzoirlty