168 REPORTS ON THE STATE OF SCIENCE.—1913. 
Note 30. This Note relates to the efficiency of a gas engine with 
varying degrees of compression, and is embodied in a paper which 
is to be presented at the Birmingham Meeting of the Association. 
Note 31. This Note, presented by Dr. Clerk, relates to experiments 
on the determination of the specific heat of gases, with special relation 
to the correction applied to eliminate the effect of the small amount of 
leak of charge. 
Certain of the More Complex Stress Distributions in Engineering 
Materials.—Report of the Committee, consisting of Professor 
J. Perry (Chairman), Professors EK. G. Coxser and J. E. 
PETAVEL (Secretaries), Professor A. Barr, Dr. C. CHREE, 
Mr. GILBERT Coor, Professor W. EK. Datpy, Sir J. A. Ewina, 
Professor L. N. G. Finon, Messrs. A. R. Fuuton and J. J. 
GuEsT, Professors J. B. HENDERSON and A. E. H. Loves, Mr. 
W. Mason, Sir ANDREW Nose, Professor KARL PEARSON, 
Messrs. F. Rocers and W. A. Scosiz, Dr. T. EK. STANTON, 
and Mr. J. S. Witson, appointed to report thereon. 
Report on Combined Stress. By W. A. Scostz, B.Sc. 
INDEX. 
PAGE 
Historical : 4 é 5 = : : < : : : ‘ ; sve 168 
Theories . 5 4 3 5 5 5 ; > : é ‘ F : : i 169 
Failure . : ; : : ; 2 : : 2 : 2 : : : —xe LTO 
Materials F P : : : : : ; : : ; : ‘ : ~  L0 
Systems of Stress . Rha TSS EO eee eld a 
Rate of Loading and Repeated Loading . ei job's 3 Sen [3 tg Mie ieee 
Mechanism of Failure . 5 : é ; : . : ‘ ore UT 
Early Engineering Tests . LMR <) copes 5 
Experiments with Ductile Materials under Combined Stresses : efit ey 2 
Brittle Materials under Combined Stresses . . . . . «. . « I75 
Friction Theory . eee i ea Se eC ere Pre eS eed lS 
Liider’s or Hartmann’s ‘Lines : 3 ? : 2 ae Te 
Some other Considerations in Combined Stress Researches : : : : 2 3-176 
Alternating Combined Stresses su! sey at ie ee ar ee et Set ee ed 
Separationiof Materials... jt > APs sche adele ears an asta (toe 
An Mngineering Views.) ) iy es sks) tees clei ek 0) Bitte hol a 
Conclusion . a Leo 
(The sina eile t in the t text role to the bihlionea phy ) 
Historical—Coulomb 1 appears to have been the first to study the kind of 
strain we now call shear, and he considered that rupture takes place when 
the shear of the material is greater than a certain limit. This is the first 
recorded Theory of Strength, but since it refers to rupture, the shear 
defined is a permanent set. Vicat® drew attention to the flow of metals 
when he discovered that the yield of iron is dependent on the time it is 
stressed, but Tresca,® by his extended researches, kindled great interest 
in this subject, and he also stated that the maximum difference of the 
greatest and least principal stresses is the measure of the tendency to 
rupture. Theories of molecular action were devised by various investiga- 
tors to account for the viscosity and the elastic afterworking.* Love 
* See The Mathematical Theory of Elasticity, Love, 2nd edit., p. 116. 
