IO WALTER H. BUCHER 
Hartmann’s observation that the angle of shearing is independent 
of the nature and intensity of the stresses involved. 
It also brings out clearly, in a qualitative way, the very different 
attitude of the planes of shearing in brittle and ductile substances. 
This becomes apparent when we introduce into it the average 
values of ultimate strengths contained in the following table: 
TABLE I* 
ki 
Tons, |) Se 
Granite (Gv) 50o> cae ee eee ToS Ou 25 
Glassi(vaniousysorts) hens amin cone oe eno 4.3-8.7 | 2.5-6.0 | I5-— 
Mila oles (avs): vevce te arcs cpnisy oka cer eles emieietees chek enone 4.0 Ona5 II 
HBIVEeSton ess rye cathe i CR nes aha a 6.8 0.7 9-7 
AGES tOMe{(Givia) ees. eseoks eke UCI nee Bo On 5 7 
Glassi(Comimontereen) saree eeceeeennee Bio) 1.5 6.7 
OMe (CASTS cele ee ral cre ae Ns Rete ie era Re 40 Fo 5 Ga 
ZAM CRCAS tea 4 discrete: coat ccrecaye Muosine AREA SIS moon (10) 2.5 (4+) 
Georgia Yellow Pine (across grain)............... On7] 0.3 Doe 
Coppersicastaytin sn acce oka o eri em nea (20) - 12 a9 
LEST SCS) Ga ta ety tar eaten Sen A ee ans toa. Ole eet Ee aR 35 I 
Coppers sOlis eee A. LA ies tuahn poole iter myeaiie ae 15 15 I 
SIUC CR rae sR Gera, Magee Mm gene Mec ecc a 5 5 I 
Winhitei@aks(Gicrossiorain) seen eeee einer I I i 
Wiarter@alker (yatiny esa) peepee er ane ee 3.5 5 0.7 
Iron, wrought (av. good bars)................... 16-20 25 0.6-0.8 
Georgia Yellow Pine (with grain)................ D5 6 0.4 
* All figures in this table, excepting those in the third row, from H. H. Suplee, The Mechanical 
Engineer’s Reference Book (4th ed., 1913). 
They represent at best only average values and are used here only in a qualitative sense. Values 
of K2 given in parenthesis indicate loads producing 10 per cent reduction in original lengths. 
All figures are given in the original in lbs. per sq. in. 
The values for various sorts of glass are taken from Winkelmann and Schott, quoted in O. D. 
Chwolson, Lehrbuch der Physik, Vol. I (Braunschweig, 1902), pp. 709 and 712. 
} ‘Fine-grained, compact, very strong and durable” graywacke (of Hamilton age). G. P. Merrill, 
Stones for Building and Decoration (2d ed., 1897), p. 322. 
According to the formula, the angle 6 will differ the more from 
go the greater the ratio of the values of crushing and tensile 
strength. 
Correspondingly, we find that substances like glass shear at 
very acute angles,t while for mild steel the angle varies between 
80° and 100°.? 
 20°-30° in the case of glass of thick microscopic slides, according to tests made 
by the writer. 
2 See results of experiments by W. Mason and G. H. Gulliver, as given in 
W. Mason, “The Liiders’ Lines on Mild Steel,” Proc. Phys. Soc. of London, Vol. XXIII 
(1911), p. 306. 
