88 SEC. 3. MEASUREMENT. 



434. Flexion Pandynamometer. An instrument designed 

 to determine the work done by a steam 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 a non- elastic 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 graduate, 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 th 

 cylinder. 



435. Torsion Pandynamometer. This instrument is 

 designed to measure the "power supplied to an engine or 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. The axes of these pinions govern by 

 their extremities, which are directed towards each other, the four bevelled 

 wheels of an ordinary differential movement. The two intermediate wheels of 

 this movement are loose on a shaft, which is continued 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 propor- 

 tionate to the torsion to which the shaft is subjected. At the upper and loose 

 extremity of the steel rod is secured, by means of a hinge, a horizontal and 

 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 motive 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 day's work, two 

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

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

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

 weight. 



Simple proportion then gives the weight, 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. 



