THE STEAM-ENGINE. 165 



the arm is on one side of the spindle; if we imagine the arms 

 produced until they intersect the axis of the spindle, we shall 

 see that when the balls go up, the point of intersection of the 

 arms with the spindle comes down, and in that way the vari- 

 ation in the vertical height of the governor is much greater 

 than when the joint of the arms is made in the line of the 

 spindle itself as in the Watt governor. But Mr. Head im- 

 proves upon the Watt governor ; he takes the arms through 

 the spindle and pivots them on its opposite side ; so that 

 when the balls rise, the point of intersection of the arms with 

 the spindle rises also, and that governor, therefore, will act 

 with comparatively little variation in its effective vertical 

 height. 



Then we have Dr. Siemen's chronometric governor, which 

 acts as an absolute regulator, and we have also Dr. Siemen's 

 liquid governor, which also operates with absolute regularity. 

 I am only sorry it is impossible to enter into a description 

 of them. 



Passing from this subject ; there are two things which in 

 these days everybody knows all about ; one is the wire-drawing 

 of steam, and the other is the freeboard of a ship. I am 

 not going to say anything about the latter, but in regard 

 to the wire-drawing of steam there is among the " every- 

 bodies " the strongest possible notion that it is a thing to be 

 deprecated. But far from it, in the ordinary construction of 

 bad engines, of which we have so many, wire-drawing is really 

 a thing to be admired. Consider the case of an engine 

 without any expansion valve, a cylinder far too large for 

 its work, with a governor having a throttle valve very 

 nearly closed, and with the steam going into the jacket of 

 the slide valve, and accumulating there until the valve opens 

 to let it into the cylinder. During the time the crank is 

 near its centres, and the piston is going slowly, then notwith- 

 standing the orifice for the inlet of the steam is restricted, an 

 accumulation of steam in the slide jacket is obtained so that 

 at that time the pressure there approximates to that in the 

 boiler ; when the slide valve opens that pressure comes upon 

 the piston, and thus we get a sort of irregular, very bad ex- 

 pansion diagram as the indicator figure ; but for what you do 

 get it is of value. On this point I must call your attention 

 to Diagram 1 3, in illustration of what may result from wire- 

 drawing in an engine demanding a mean pressure of 27 Ibs. 



