658 



MB. C. W. SIEJME^'S ON UNIFORM KOTATION. 



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 Fig. 1. 



by dotted lines in 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 

 wliich 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 govemor-balls suifices to 

 overcome the friction of the valve and its mechanical connexions, which are not incon- 

 siderable. In the mean time the speed of the engine will have been increased to an 

 extent considerably beyond what is required in order to maintain the valve in its new 

 adjustment; the action of the governor, Avhen it does take place, will therefore be 

 excessive, and a series of fluctuations in the speed of the engine must follow before the 

 proper readjustment of its valve can be effected. 



Chronometric Governor. — Impressed with these imperfections in Watt's centrifugal 

 governor, I proposed, twenty-three years ago, in connexion with my brother, Werxeb 

 Siemens, a governor based also on the conical pendulum, which in this case was to be 

 independent in its action of change in its angular rotation, and, moreover, was to be 

 provided always with a store of power ready to overcome the resistance of the valve at 

 the first moment when the balance between the power and load of the engine was 

 disturbed. This instrument (the chronometric governor) has been applied with suc- 

 cess in many cases where engines were required to work with great regularity under 

 varying conditions of load ; it has also received an interesting application by the Astro- 

 nomer Eoyal for regulating astronomical and chronographical instruments, proving 

 the high degree of precision of which it is capable. 



The leading idea involved in this governor consisted in providing a conical pendulum 

 in uniform rotation, and in establishing a differential motion between it and the wheel 

 driven by the enghie, which difierential motion was made to act upon the source of 

 power of the latter. If this idea could be cai'ried out, it was evident that the engine, or 

 machine to be governed, must suit its motion closely to that of the independent rotating 

 pendulum, because the least retardation on its part must immediately result in an 

 enlargement of the valve-orifice (it being understood that an increase of available power 



