Page:The Kinematics of Machinery.djvu/222

200 rolling mills, where formerly the fly-wheel was considered a sine qua non. There was a necessity for reversal in the case of the plate mills, but the application of chain-closure there seems to have led to its use in other cases where no such necessity existed. Coupled engines are used for non-reversing factory engines also, — locomotives and marine engines may have suggested the arrangement, while its own intrinsic value has confirmed and extended its adoption. In blowing-machines, too, no less than in steam-engines, we see the same thing; by increasing the number of cylinders, by adding separate regulating cylinders having pistons driven by cams, as well as by other arrangements, frequent endeavours have been made to substitute chain-closure for force-closure. We have unquestionably in all these things a distinctly recognisable tendency shown towards certain alterations of older machine-forms into others which furnish more direct solutions of the actual problem, the production of certain determinate motions.