AMERICAN INSTITUTE. 607 



although they have been much used in this country and in 

 France. 



In 1840, the link motion was introduced, which, by its sim- 

 plicity and elegance, rapidly obtained favor, and came into use. 

 This gave a variable expansion, which greatly increased the eco- 

 nomy effected by the previous improvements. But the distribu- 

 tion effected by the link is not generally conceded to be all that 

 is desirable J it is objected that it releases the steam too early 

 when it cuts off" early; that it shuts the exhaust too soon, and 

 thus causes compression ; that it does not cut off early enough, 

 without carrying these faults to excess; and that it wire-draws 

 the steam too much whenever it cuts off at an early period. Mr. 

 Septimus Norris speaks of it as a good means of reversing, but 

 not as a good expedient for cutting off. Mr. Bates, of the New 

 London and Willimantic railroad, has got up a supplementary 

 valve to relieve tlie engine from the compression that attends the 

 link. Mr. Corlies has constructed a valve movement, as differ- 

 ent as possible from it, to avoid its compression, its early release, 

 and to give a wider opening to the ports ; and others, less known, 

 have labored to produce something better. 



The theory of these reformers is, that the steam should not be 

 admitted until the stroke commences; the port should then open 

 suddenly to its full width. When the time for cutting off ar- 

 rives, the port should be suddenly closed; and at the' end of the 

 stroke, the exhaust port should be suddenly opened to its full 

 width, and the quicker these movements take place the better, 

 provided there be no concussion in the valve gear. The link 

 party, which is ably represented by Mr. D, H. Clark, reply that 

 these defects of the link are not without compensation, and not 

 in themselves so great as many deem them ; the admission is am- 

 ply sufficient when the cut off is late ; and when it is early, the 

 wire-draw is but slightly objectionable, because not much power 

 is wanted ; as to the premature release, it occurs only at high 

 speeds, when the steam has not time to lose much pressure be- 

 fore the end of the stroke, as the diagrams show, and the com- 

 pression helps to make steam for the next stroke, and cushions 

 the piston, and arrests its motion gently, which is desirable 

 whenever the joints are loose. This last argument, however, is 

 seldom adduced. Clark does not adduce it, and I do not find 

 much authority for the opinion that the joints, when pi-operly 

 keyed up, required such means to prevent them from beating. 



I am of opinion that the link is the best motion yet introduced, 

 for engines that run at high speed; but I still think the objec- 



