BAA REPORT—1896. 
TABLE II.— Continued. 
| Mean for} Deviation from S8 
ia Greatest Least. \ninter-| mean of Pata 
Re ar extension |exten-ion| 01, 4 each Per cent sea 
Observer 'No.! in Interval of 23 y ». |deviation |2.2 3 
| aieaea | eich observer’s oto 
4 observer results a 3 = 
= | =. i] 
| ee tel WHS: Yo fe +-000094 | 6:09 
_E | -001638 001447 | 001544 | 7 Goggg7 cal 6-18 
W.c.U... .| B | -001852 |.001418 | -001485 Bee pia 451 
(Lever extenso- aeq | + 000032 5°54" 
- 7 . 9 iy 9 . ‘ ys) = . 
meter) E | -001293 |-001217 | 001261 — Soo0014 | 350 3-02 
= oilvemienee|tnt 0008s | |) MzeaaNln ls 
ars Cae A | -00190 }00185 | 001855 | * Soog95 | o27 f| 1°35 
fe Lapua Olleaa@iaecctere COOOKS |) iia 
| fap 00430 | 004345 | > ooooas hg 115 
eee Gi crag | +:000010 | 0-477}. 
| L |,-00215 00210 | 002140 | * oooo4g | tary) 1:70 
I]. ha o1ox | +°000075 | 353 
| | 00220 00195002125 * “oooi75 398 f 588 
, 003088 | + 000012 ees ; 
| ( 00310 | 00300 | 003088 | Oooggs 9-35 [| 1°62 
|; eg me en eae Ro 3:23 
| E | a Looiso |-oo1ss | 7 DNa0e 323 f 3:23 
a at (thiolase Cath oc OOOH 3:23) | 9. 
00160-00150 | -oo155 | *‘O00NS ae \ 3-23 
ar kolck 00002. 1°33 1 | o. 
By} 0019 © 0018 "|'-001875 | Nanas | og i 2°66 
hanes Pyavat “NN91% + 000046 2°13 . 
ws (0022-0021 Ofz16e noosa | oes 
is aacts (alte +-000054 | 251 
{70022 — }00205 "002146 | Foe | a art 3-49 
Tt will be seen that the deviations of the maximum and minimum 
values of the extension for 1} ton (or 25 tons) from the mean value are 
somewhat considerable, and often exceed 5 per cent. ina 
Tn considering the apparently large percentages of error in some cases. 
in this table, it must be remembered that the extensions were measured 
for a comparatively small increment of stress ; also that the greatest and 
least extensions of each observer are those probably affected by the largest. 
accidental errors. 
Ill. Method of finding the Mean Extension for a given Increment of 
Load from which the Coefficient of Elasticity is calculated. 
Tf a series of extensions are observed for a series of equal increments 
of load, and if the coefficient of elasticity is constant for the whole range 
of stress to which the bar is subjected, then the arithmetical mean of the 
observed extensions is the true mean extension according to the observa- 
tions for the given increment of load. It is this mean which should be 
used in calculating the coefficient of elasticity. Also, apart from mere 
observational errors, the value of the mean extension will in no wa 
depend on the magnitude of the increments of load for which the exten- 
sions are observed, * 
Tf, however, the coefficient of elasticity is not constant for the range 
