170 FERGUSON'S LECTURES. 



LECT * ne cock when required. This cock is constructed precisely in 

 V. the same manner as other cocks for fluids, and consists of a 



^"V"X^ conical plug or pin ground very truly into the body of the cock 

 itself, but instead of having a single straight passage through the 

 plug, as is commonly the case, there are two curved ones h and i, 

 which give the plug the appearance of having four openings, 

 each appearing in the same plane, and at one quarter of the cir- 

 cumference apart, so that as the cock stands in the figure, steam 

 coming from g would pass through the opening i in the plug, 

 and would be delivered into the pipe n at right angles to its first 

 direction, instead of passing directly onwards to o, as would be 

 the case in a common cock. From the pipe n the steam would 

 pass immediately into the lower part Z of the cylinder, and con- 

 sequently would drive the piston upwards. At the same time it 

 will be seen that there is an immediate connection between the 

 upper part Y of the cylinder through the pipe m, and opening h 

 of the cock to the pipe o o, leading down to the condenser ; con- 

 sequently, so long as the steam is acting against the under side 

 of the piston, there will be a vacuum at Y^to permit it to rise. 

 So soon as the piston has arrived near the top of the cylinder, 

 the cock must be turned one quarter round by depressing its 

 handle p from its present position to that shewn by the dotted 

 lines at q, by which all the openings in the plug of the cock will 

 be changed: steam, therefore, which now enters at g will be 

 turned upwards by the passage h, and by entering the pipe m 

 will be conveyed above instead of below the piston, while the 

 passage i forms a connection between the pipe n, leading to the 

 lower part of the cylinder, and the pipe o leading to the con- 

 denser ; consequently in this position, a vacuum will be formed 

 below the piston, while the steam is operating above it. The 

 piston will therefore descend, and on coming near the bottom, 

 the cock must be again turned into its first position, when the 

 piston will ascend, and so on ; thus producing an equality of 

 force, both in the up and down strokes, by simply turning one 

 cock, an operation that is effected by the motion of the beam 

 without any other assistance. Vide PROFESSOR MILLINGTON'S 

 Lectures. 



The governor is a very important part of the mechanism of 

 a modern steam engine, and the simple arrangement of its parts 

 may be readily explained by reference to the annexed diagram. 

 A square iron rod a b, with pivots as its two ends, is fixed up 

 in a vertical direction in any convenient part of the engine 

 house, so that it can revolve on its axis in proper bearings, 



