THEORY OF THE REFLECTING EXTENSOMETER, 101 
the graduation of the scale itself hardly warrants any attempt to 
further refine the measurement. 
TABLE I. 
Corrections to Scale-readings, the zero being in the position of 
adjustment, Z 1135 mm., and 7 4°54 mm. 
Seale Approx. Distance EZ between contacts on test piece in 
Reading. Angle. illi 
2w 
30 50 100 150 200 
mm, mm. mm. mm, mm, 
*, 0. CG 00 ‘00 ‘00 00 00 
50 9: +05 +01 ans “OE — 02 — 03 
ee +12 +09 +06 +05 +05 
1 9 — 04 —-09 —-19 x +99 — 24 
cts +62 +49 +°39 +°36 +34 
l ne — +23 = BS — 75 — ‘83 — 86 
aa, Ac98 +172 + 1°42 +1:20 +112 +1-09 
20 209 OLAS 24 90-2968 « “2908 
weg Ag +359. 43:07 - 42°68 - 42:55 © +249 
+ 25 ; wd) LBS cas Blo owed i eae 
ht +643 +562  +4+5°02.. +482 +472 
+ 300 14: i468 =. - -89... ~ 667s ~ 6965. =P 
pao +1038 +994 +4839 +810 +7:95 
+ 350 17- =797 ~.9:50 «1064. ~1103..— 1131 
bs +1559 +1407 +12:93 +412°54 +12°35 
+ 400 19- =~1943 -14-:37 =J684 =<16°55:- <—i1007 
iis +22:19 +2023 +1877 +1828 +18°03 
+ 450 21-38 —18:13 -20°55 -—22:36 -22°97 - 23-27 
+30:22 427-31 +2599 +425:39 +2508 
+ 500 23- —25:16 ~—28:07 -—30-:26 -—30:99 -31°35 
sie +39:73 +3681 +3463 +33:90 +433°54 
Norz.—The upper signs are to be taken throughout in extension tests, 
; : y in 
relation to the sign of the correction. That is to say, a plus correction 
numerically reduces a minus reading. 
When the mirror is on the further side of the test-piece, an 
extension causes a reduction instead of an increase of the distance, 
from the point where the sight-line meets the mirror, to — 
That is to say IM” instead of being positive as shewn in Fig. i 
