108 THE SCIENTIFIC PAPERS OF 



upon permanent change of speed of the engine, the name of 

 " governor " seems inappropriate, the instrument being, in fact, 

 only a " moderator " of the amount of fluctuation to which the 

 engine would be subjected without its agency. The amount of 

 these fluctuations depends, in a great measure, upon the mechanical 

 construction of the instrument, which is, generally speaking, very 

 objectionable, inasmuch as the pendulous arms are mostly sus- 

 pended at points beside the common axis of rotation, giving rise 

 to an increased variation of time for a given change of angle ; the 

 reason being that the true pendulous length has to be measured 

 from the point of intersection of the pendulums or rods with the 

 axis of rotation, which point descends as the angle increases, 

 causing the pendulous length to diminish at both extremities. A 

 better result would be obtained if each pendulous rod were 

 suspended from the point past the axis of rotation (as shown by 

 dotted lines in Plate 19, Fig. 1), causing the two rods to cross in 

 the line of the axis at a point which would rise with increase of 

 angle, and render the true pendulous length approximately uniform 

 between certain limits. 



The governor of Watt is, however, subject to another defect 

 which does not admit of an easy rectification, and which consists 

 in its want of power to operate on the steam-valve at the moment 

 when the equilibrium between the power and load on the engine 

 is disturbed. It will be seen that while the engine proceeds 

 uniformly, gravitation and centrifugal force must be in equilibrium 

 as regards the governor-balls, but at the moment when, for instance, 

 a portion of the load on the engine is removed, steam-power will 

 be set at liberty for accelerating the fly-wheel. This acceleration 

 proceeds in accordance with the well-known gravitation laws until 

 the increase of centrifugal force imparted to the governor-balls 

 suffices to overcome the friction of the valve and its mechanical 

 connexions, which are not inconsiderable. In the mean time the 

 speed of the engine will have been increased to an extent con- 

 siderably beyond what is required in order to maintain the valve 

 in its new adjustment ; the action of the governor, when it does 

 take place, will therefore be excessive, and a series of fluctuations 

 in the speed of the engine must follow before the proper readjust- 

 ment of its valve can be effected. 



CHRONOMETRIC GOVERNOR. Impressed with these imperfections 



