1 1 SEC. 3. MEASUREMENT. 



434. Flexion Pandynamometer. An instrument designed 

 to determine the work done by a stearn engine, by means of the 

 flexion of the beam. G. A. Him. 



On the upper edge of the beam is a rigid wooden bar of the same length, 

 resting in the centre on a fork which prevents it from swerving, fastened to 

 one end of the beam with an iron rod, and free at the other end. To this 

 extremity is attached an inelastic cord, which passes round a pulley, fixed 

 at the head of the beam, and is carried thence towards the centre, where it is 

 wound round the axis of a very light needle. 



It is evident, from this arrangement, that when the beam moves in either 

 direction, the end of the wooden bar which remains rigid approaches to or 

 recedes from the head of the beam. The cord consequently winds itself 

 round, or unwinds itself from, the axis of the needle, and the deviation of the 

 latter indicates the degree of flexion of the beam, multiplied if desired. At 

 the end of the needle is fixed a pencil, which works on a small board placed 

 above the beam. This pencil, at each double stroke of the piston, traces a 

 closed curve, of which the ordinates indicate the successive degrees of flexion 

 of the beam during the work. To determine, once for all, the degree of 

 flexion corresponding to a given load, the crank of the fly-wheel should be 

 fixed at the dead point, and steam at a known pressure should be introduced 

 into the cylinder. 



435. Torsion Pandynamometer. This instrument is de- 

 signed to measure the power supplied by an engine to a factory, 

 by means of the torsion of the shafting through which the motive 

 power is transmitted. G. A. Him. 



At the extremities of one length of the shafting are keyed two toothed 

 wheels of equal diameter, which gear, one directly and the other by an inter- 

 mediate wheel, into two smaller pinions. These pinions gear into the four 

 bevelled wheels of an ordinary differential movement. The two intermediate 

 wheels of this movement are loose on a shaft, which is prolonged in a vertical 

 direction, and made of a light steel rod. The result of this arrangement is, 

 that if the shaft twists, this rod deviates, and forms with a vertical line an 

 angle proportionate to the torsion to which the shaft is subjected. At the 

 upper and free extremity of the steel rod is seciyed, by means of a hinge, a 

 horizontal very light wooden bar, carrying at its extremity a roller, to which 

 is attached a recording apparatus. This roller, when the shaft is at rest, lies 

 in the centre of a wooden disc covered with paper, and revolving uniformly 

 on a vertical axis. 



So soon as the steel rod deviates from a vertical line, in consequence of the 

 torsion of the driving shafting, the roller leaves the centre of the disc, and 

 begins to revolve. The turns registered by the recording apparatus are exactly 

 proportional to the torsion of the shafting. 



The mean torsion of the shafting being thus known for a clay's work, two 

 parallel levers, placed in contrary directions, are securely fixed at the extre- 

 mities beyond the two toothed wheels, and the free extremities of the 

 levers, so as to determine the deviation caused in the vertical bar by a given 

 weight. 



Simple proportion then gives the resistance, corresponding to the mean 

 angle obtained during a day's work, and it becomes easy to determine the 

 mechanical work which corresponds to this angle. 



