688 Memorandum on the Adjustment of Dynamometers. 
On plotting these data it is at once apparent that the line 
joining the ordinates is very nearly a straight line, but it cuts 
the base within the zero-point, and hence a correction, 0 5=31, 
must be added to each reading for a distance of 192 yards, or 
0'1615 per yard. 
Work done, therefore, is, say for the first trial, 
705 lbs. X 192 yds. x 3 ft. = (7(159-7 + 31) = foot-pounds. 
Then from 1st trial C = 705 x 192 x 3 ^ 2129 • 46 
190 '7 
„ 2nd „ C ^^^^^l-^l = 2nQ-iQ 
loO'S 
o . n 3G9 X 192 X 3 „, 
„ 3id „ C= =2136-21 
2132-15 mean. 
Results which, it will be seen, agree very well together. 
The general, equation for these springs is : — Work in foot- 
pounds = 2132 (reading of index + 0-1615 Xyards). 
We may remark that plain spring-links, and the diagrams 
traced by the dynamometers, are capable of giving very limited, 
and frequently very deceptive, information. They are only 
useful in indicating the maximum and minimum pulls, or excep- 
tional efforts at particular places. It is almost impossible to 
calculate the mean draught from a diagram, owing to the exccs- 
, sive waviness of the line ; and it is not easy to note the extreme 
positions of the index of a spring-link, on account of the quick- 
ness of the motion. On the other hand, the integrating counter 
can be specially noted between any two points of a run, and the 
mean pull deduced from it. It is found that the measuring- 
wheel records the distance passed over very accurately, and it is 
always better, in working out the results, to assume that the 
distance recorded by the measuring wheel is correct, though it 
may differ from the actual distance ; because if there is any slip, 
there is also a corresponding reduction in the integrating counter. 
We need hardly observe, that the values of C and p may be 
obtained from any two trials, by solving them as simple equations 
with two unknown quantities. 
