Page:The Kinematics of Machinery.djvu/258

 could be paired with the wheel, all indicating the general tendency towards the limitation of force-closure. Thomson's India-rubber tyres have essentially the same object; the inner side of the ring of vulcanised India-rubber, externally flattened upon the road, serves as a smooth uniform surface for the rigid tread to run upon—thus corresponding generally to the rail of the railway.

The development of the Turbine has followed the same course;—it has grown out of the primitive wheel of the Tyrolese and Swiss mountaineers in the hands of the mechanicians of our century. In the latter the water dashed and eddied against its irregular blades in vehement force-closure;—in the Turbine it is already combined into a pair of elements with the accurately shaped wheel with very considerable completeness. The progress of instruments for breaking stone into small fragments, from the ancient stamp to the crushing rollers with which we were so long content, and then almost abruptly to the stone-breaking machine, without which to-day a blast furnace would scarcely be thought complete,—has been from closure by sensible forces in the mass alternately lifted and allowed to fall, to closure by the latent forces of a system of cranks and levers. There are many old iron-works which have seen the transition from tilt- and lift-hammers to their present crushers, rolls, and forging-presses.

The still young agricultural machine industry is attempting the very difficult problem of superseding, or at least limiting, a very complex force-closure by pair- and chain-closure.

. 177.

How much we are still engaged in replacing force-closure by kinematic closure, and how strongly we feel in the matter that we are striving after something new, trying to reach a better position, the hydraulic press, invented at the end of the last century, shows.