T. GRAY AND J. MILNE ON JAPANESE ROCKS. 139 



10. On the Elasticity and Strength- constants of Japanese Bocks. 

 By Thomas Gray, Esq., B.Sc, E.B.S.E., and Brof. John Milne, 

 F.G.S. (Bead November 2, 1881.) 

 (Abridged.) 



This paper contains a description of experiments made for the 

 purpose of determining the different moduli of elasticity, and the 

 strength against rupture and crushing of some of the more common 

 Japanese rocks. One main object of the experiments was to obtain 

 data for the calculation of the theoretical velocity of propagation of 

 earthquake-waves, and by comparison of this velocity with the results 

 of observation, to gain some idea of the degree of continuity in the 

 strata. 



The experiments on the moduli and the rupturing strength were 

 performed on round columns of the rock about 4 centimetres in 

 diameter and 60 centimetres long; those on strength against 

 crushing were for the most part made on round columns 4 centi- 

 metres in diameter and 12 centimetres long. 



The Young's modulus of elasticity was calculated from the results 

 of experiments on cross bending, the columns being supported at 

 both ends. 



The modulus of rigidity was calculated from the results of 

 experiments on the torsion produced by the application of measured 

 twisting motives. 



The bulk-modulus was calculated from the known relation between 

 it and the Young's and rigidity-moduli. 



The modulus of rupture was found by observing the load required 

 to rupture the column by cross bending. 



The experiments on crushing were performed by means of a 

 Bramah's press, the pressure being estimated by means of a 

 Bourdon's gauge. 



The following Table (p. 140) gives the results of the experiments ; 

 the headings of the different columns sufficiently explain their 

 contents. 



Discussion. 

 Bev. E. Hill thought that the results obtained might have 

 another application. In studying faults and joints, the elasticity 

 and capability of resisting crushing of different rocks must neces- 

 sarily often be taken into consideration ; and for such a purpose the 

 determinations made by the authors might be of great service. 



