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XXIV. — Memorandum on the Adjustment of Dynamometers. By 
Messrs. Eastons and ANDERSON, Consulting Engineers to 
the Society. 
During the many years that the Royal Agricultural Society has 
used registering dynamometers, for testing the power required to 
work various implements, difficulties have from time to time 
arisen, in getting the instruments to record accurately and con- 
sistently with the laws which are supposed to govern their 
action. This has been even more evident in the communica- 
tions that have reached us from foreign countries, and from other 
Societies for whom we have made dynamometers similar to 
those used by the Royal Agricultural Society. 
The introduction at the Bedford and Taunton Implement 
Trials of the horse-dynamometer, the most complete and accurate 
instrument we have yet made, and which is fully described in 
the 'Journal,' Vol. X., 2nd Series, p. 680, induces us to offer 
a few remarks on the adjustment and use of dynamometers, 
and the mode of determining their co-efficients ; and in doing 
so we must begin by stating how very much we are indebted to 
our Chief Engineer, Mr. W, E. Rich, for solving the difficulties 
connected with the use of these invaluable instruments, his great 
practical experience in the trial-fields, having given him a 
thorough insight into their peculiarities. 
The registering apparatus, as is well known, consists of a flat 
disc, moved by a wheel, which measures the distance traversed ; 
the number of revolutions made by the disc is, therefore, in pro- 
portion to the distance passed over by the instrument. Across 
the face of the disc, and exactly in the line of its diameter, a 
small integrating wheel, as it is called, traverses, the wheel 
being at right angles to the disc, and kept in close contact 
with it by a spring, and caused to revolve by the friction of its 
periphery against the face of the disc. This wheel actuates a 
counter, and is connected with the spring or springs through 
which the draught or driving-power passes, so that the wheel 
moves from the centre of the disc towards its periphery, as the 
draught-springs yield under the power applied : and as the cir- 
cumference of a circle bears always a constant relation to its 
diameter, it follows that the further the wheel is from the centre 
of the revolving disc, the faster it will turn ; but if the inte- 
grating wheel is adjusted so as to be exactly opposite the centre 
of the large disc when the springs are unloaded, its distance from 
the centre, and therefore, also, its number of revolutions per 
revolution of the large disc, will increase in direct proportion 
with the strain applied, and the revolutions of the large disc are 
2 Y 2 
