264 OF THE REGULATION AND [SECT. vm. 



the point of suspension above the plane of revolution at the mean velocity. 1 Thus, 

 if the mean height be 39-14 inches, then one-tenth on each side will be 



39-14 + 3-914 = 43-054 

 39-14 - 3-914 = 35-226 



One-fifth of 39- 14 = 7-728, the range. 



Where a throttle valve is acted on by a governor, the steam passage should be 

 fully open at the usual velocity of the engine, and contracted only when it exceeds 

 that velocity, otherwise the steam must be always throttled, except when the 

 engine is working against an unusual resistance. 



553. The balls are made from 30 to 80 Ibs. each ; their effect, however, 

 depends considerably on the angles formed by the combination of bars. In the 

 form in Fig. 1. Plate vm. the force is small, but the quantity of motion is con- 

 siderable ; while that in Fig. 3. Plate xv. has more force and less motion. The 

 angle the ball rods make with the axis, should be about 30 when they are at 

 rest ; and provided the range be sufficient, the angle the connecting rods make 

 with the axis, may be made acute with advantage in point of power. * 



554. The velocity of an engine for raising water has in some instances been 

 regulated by a small cylinder provided with a piston, and fixed on a pipe from 

 the air vessel of the main ; which, when the engine goes too quick, forces water 

 into the lower part of the small cylinder, and raises its piston. The piston is 

 loaded with a weight corresponding to the proper velocity of the engine, and 

 therefore it is only when it goes too rapidly, that, the friction increasing in the 



1 For if v be the mean velocity, and it increases to v + n v = v (1 + n) ; then the height of the 

 plane of revolution will be altered from h to ^ ^ ; or in the ratio of (1 + ) 2 : 1, consequently, 



the change in the velocity will be to the change in the height of the plane of revolution, as 

 1 + n : (1 + n) 2 ; and the increments are as : 2 + *, or as 1 : 2 + n ; and when is a small 

 fraction, it is nearly as 1 : 2. 



From want of attention to this point, the governor has been supposed to be deficient in sensi- 

 bility to the changes of velocity in a nice machine ; and M. Preus has proposed to use a small 

 pump to raise water to a cistern, from whence it escapes by an aperture which can be regulated at 

 pleasure. When the engine moves at a greater speed than the proposed one, the water rises in the 

 cistern, and raises a float which closes the throttle valve. See Phil. Mag. vol. Ixii. p. 298. It is 

 obvious that it cannot exceed the governor in sensibility, while it will require considerable atten- 

 tion to keep it in order. 



* Several trials have been made to apply the governor to boat engines, but it appears to me 

 that the changes are too sudden for this mode of regulation. 



