Page:The Kinematics of Machinery.djvu/255

 all cases to form an opinion about matters occurring in our own time, for we ourselves are subject to the influence of the time, and must judge it while we form part of it. The immense number of cases existing, on the other hand, and the exactness of our knowledge of them, here help us very greatly. An examination of the way in which the gradual perfecting of machines is to-day going on teaches us, however, one thing,—as we shall presently see,—namely, that

. 175.

In Newcomen's steam-engine, Fig. 174, force-closure still predominated, and it remained thus through the whole eighteenth century. The machine was force-closed in its pit-work, in its beam-chains, in its steam-piston and in its valve-gear, although in the latter Potter's invention had substituted a machinal arrangement