THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



SEPTEMBER 1891. 



XXXIII. Some Applications of Physics and Mathematics to 

 Geology. By C. Chree, M.A., Fellow of King's College, 

 Cambridge*. 



Part I. Some Physical and Mathematical Data. 



MANY of the terras employed in treating of the properties 

 and conditions of matter have in common use a some- 

 what vague meaning. The meaning, so far as clearly outlined, 

 is also only too often different from that which the physicist 

 intends to convey. As regards terms such as rigid, solid, 

 plastic, viscous, &c. it seems to me that even eminent geologists 

 are apt to he misled by the popular usage, so that they fall 

 into error respecting the data which mathematical and 

 physical science places at their disposal. It thus seems 

 advisable on the present occasion to clear the ground by 

 briefly considering the sense attached to these terms by the 

 more exact school of physicists. To render the following 

 statements intelligible it is necessary to explain the meaning 

 scientifically attached to the terms stress and strain. By 

 stress is meant a force referred to unit of area of the surface 

 across which it acts, by strain the increase in the distance 

 between two material points divided by the original distance. 

 For instance if a vertical bar n square inches in cross section 

 fixed at the upper end, sustain a load of t tons, and the load 

 be uniformly distributed over the cross section, the longi- 

 tudinal stress is tn, taking the square inch as unit of area 

 * Communicated by the Author. 

 Phil. Mag. S. 5. Vol. 32. No. 196. Sept. 1891. R 



