THE STEAM-ENGINE. 463 



By this expedient, however the evaporation of water in the boiler might 

 vary within practical limits, the supply of steam to the cylinder would be 

 rendered regular and uniform. If the boiler became too active, and produced 

 more steam than was necessary to move the engine with its load at the re- 

 quisite speed, then the throttle-valve was shifted so as to contract the passage 

 and limit the supply of steam. If, on the other hand, the process of evapora- < 

 tion in the boiler was relaxed, then the throttle-valve was placed with its edge \ 

 more directed toward the steam. Independently of the boiler, if the load on 

 the engine was lightened, then the same supply of steam to the cylinder would 

 unduly accelerate the motion. In this case, likewise, the partial closing of the 

 throttle-valve would limit the supply of steam and regulate the motion ; and 

 if, on the other hand, the increase of load upon the engine rendered necessary 

 an increased supply of steam, then the opening of the throttle-valve would 

 accomplish the purpose. By these means, therefore, a uniform motion might 

 be maintained, provided the vigilance of the engine-man was sufficient for the 

 due management of the lever B C, and provided that the furnace under the 

 boiler was kept in sufficient activity to supply the greatest amount of steam 

 which would be necessary for the maintenance of a uniform motion with the 

 throttle-valve fully opened. 



Watt, however, soon perceived that the proper manipulation of the lever B 

 C would be impracticable with any degree of vigilance and skill which could 

 be obtained from the persons employed to attend the engine. He, therefore, 

 adapted to this purpose a beautiful application of a piece of mechanism, which 

 had been previously used in the regulation of mill-work, and which has since 

 been well known by the name of the governor, and has always been deservedly 

 a subject of much admiration. 



The governor is an apparatus by which the axle of the fly-wheel is made to 

 regulate the throttle-valve, so that the moment that the axle begins to increase 

 its velocity, it shifts the position of the throttle-valve, so as to limit the supply 

 of steam from the boiler, and thereby to check the increase of speed. And on 

 the other hand, whenever the velocity of the axle is diminished, the lever B C 

 is moved in the contrary direction, so as to open more fully the passage for 

 the steam, and accelerate the motion of the engine. 



A small grooved wheel A B fig. 22, is attached to a vertical spindle sup- 

 ported in pivots or sockets C and D, in which it is capable of revolving. An 

 endless cord works in the groove A B, and is carried over proper pulleys to 

 the axle of the fly-wheel, where it likewise works in a groove. When this 

 cord is properly tightened the motion of the fly-wheel will give motion to the 

 wheel A B, so that the velocity of the one will be subject to all the changes 

 incidental to the velocity of the other. By this means the speed of the grooved 

 wheel A B may be considered as representing the speed of the fly-wheel, and 

 of the machinery which the axle of the fly-wheel drives. 



It is evident that the same end might be attained by substituting for the 

 grooved wheel A B a toothed wheel, which might be connected by other 

 toothed wheels, and proper shafts, and axles with the axle of the fly-wheel. 



A ring or collar E is placed on the upright spindle, so as to be capable of 

 moving freely upward and downward. To this ring are attached by pivots 

 two short levers, E F, the pivots or joints at E allowing these levers to play 

 upon them. At F these levers are joined by pivots to other levers F G, 

 which cross each other at H, where an axle or pin passes through them, and 

 attaches them to the upright spindle C D. These intersecting levers are 

 capable, however, of playing on this axle or pin H. To the ends G of these 

 levers are attached two heavy balls of metal I. The levers F G pass through 

 slits in a metallic arch attached to the upright spindle, so as to be capable of 



