NOTES ON STATIONARY ENGINES. 37 



and at about half way along tliis part, so that its stroke is 

 about equal to the radius of the crank pin. This relievos 

 the strain upon the beam centre in a most important degree, 

 and for this reason has been sometimes resorted to, even 

 where the attendant economy was quite a secondary matter. 



In heavy driving ashore there is usually a great tendency 

 evinced towards very long strokes, six and seven feet being 

 not uncommon. This appears to bo a mistake, as often the 

 speed assigned does not reach forty revolutions per minute, 

 and under these conditions it is very difficult to insure such 

 stciidy driving as is often demanded ; in fact, it may be said 

 to be practically impossible with any great degree of expan- 

 sion in one cylinder, and consequently the compound system 

 is resorted to whenever any attempt is made towards econo- 

 mical working. The conditions imposed are not very unlike 

 those obtaining in a paddle boat, as described at the last 

 meeting. In. both cases the engines are of necessity heavy, 

 shw-woi'kirig ones, and in both cases uniformity or steadi- 

 ness in driving is a leading object. In each case an econo- 

 mical and satisfactory result is arrived at by compounding, 

 though regarded simply from the point of view connecting 

 coal bills and actual power obtained, it may be possible that 

 better results would bo obtained by expanding in single 

 cylinders to tlie same extent. As a rule it is not the prac- 

 tice to adopt an early cut-oif in compound stationary 

 engines, exceedingly common conditions specified being that 

 the lap shall equal the port, and that the port shall just 

 open wide ; those give a cut-off at about throe-quarters 

 stroke. Under these conditions, many engines are vk^orking 

 on a consumption of 2 lbs. per I horse power, the bore of 

 the h)w-pressure cylinder being dcnible the bore of the higli- 

 pressure one, and the .strokes of the two equal. 



Hitherto there appears to bo no cut-oft' motion actuated 



