1885 Journal of the American Medical Association (JAMA)  
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 is
more » ... c, b, which is longer than a c, the spring in Fig. 2 . If the same sized rods were employed for each spring, in order to exert a given force at b,
doi:10.1001/jama.1885.02390820008002 fatcat:voswyvpy2fectjogr2lzoirlty