The greater or less elongation of these
plates gives the tangential stress exerted by the driving pulley to
carry along the pulley that actuates the machine to be tested. This
elongation is registered by means of a pencil connected with the
spring plates, and which draws a diagram upon a sheet of paper. At the
same time, a special totalizer gives the stress in kilogrammeters.
Besides, the pulley shaft actuates a revolution counter, and a clock
measures the time employed in the experiment. In order to obtain a
simultaneous starting and stopping point for all these apparatus, they
are connected electrically, and, through the maneuver of a commutator,
are all controlled at once. The electric current is furnished by two
series of bichromate batteries.
The tests of traction machines are effected by means of a
three-wheeled vehicle carrying a dynamometer. The front wheel is
capable of turning freely in the horizontal plane, and the dynamometer
is mounted upon a frame provided with a screw that permits of
regulating its position according to the slope of the ground. The
method of suspension of the dynamometer allows it to take
automatically the inclination of the line of traction without any
torsion of the plates.
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