Measurement of Mechanical and Electrical Forces. 87 



spring pistons or Bourdon pressure-gauge tubes might be 

 employed to give inclination to the tangent-wheel. 



Integrating Dynamometers. 

 The disk-cylinder integrator may be applied to measure the 

 whole amount of work transmitted by shafting or belting. In 

 the case of shafting, what is called a differential coupling — that 

 is, a contrivance which transmits any motion, but measures 

 the force causing such motion — is employed to give inclination 

 to the tangent- wheel. In the case of belting, any of the known 

 dynamometers may be employed for the same purpose; while 

 a mangle-motion driven by the revolving shaft or travelling 

 band, causes the cylinder to reciprocate. Either of the methods 

 given on page 79 may be employed to produce continuous 

 growth of the integral in one direction. As the work trans- 

 mitted at any moment is force multiplied by motion, and as 

 the tangent of the inclination of the tangent- wheel is propor- 

 tional to the force, while the reciprocating motion of the 

 cylinder is proportional to the motion, the rate of revolution of 

 the integrating cylinder will be proportional to the rate at 

 which work is being done, and the whole number of revolu- 

 tions will give the whole amount of work done. If at any 

 time the force causing the motion should change sign and so 

 resist it, as is the case in an engine when there is much cush- 

 ioning, then the tangent-wheel will incline the other way and 

 take off from the record a corresponding amount of work. 



Electric- Current Meters. 

 The application of the disk-cylinder integrator to an elec- 

 tric-current meter is very obvious. Figs. 8 and 9 are two views 

 of an electric meter, in which the inclination of the magnet M 

 is effected by the electric current passing in a large coil sur- 

 rounding the instrument. The magnet M and the tangent- 

 wheel t are each fixed on the same spindle, which is vertical, 

 and which is very light and delicate. The weight of the mag- 

 net produces the necessary pressure between the tangent- 

 wheel and the integrating-eylinder C ; and as the surface of 

 each is convex, the friction resisting the turning of the tan- 

 gent-wheel by the magnet is very small. The cylinder is 

 supported in a bell-crank frame F, which can be made to reci- 

 procate along the wire TT by means of the mangle-motion m m. 

 The mangle-motion is actuated by clockwork, which may be 

 wound by the current itself when necessary, should such a 

 course be desirable. Fig. 10 shows the construction of a suitable 

 mangle-motion. The pinion can turn, but not move otherwise, 



