C. GENERAL PHYSICS. 137 



"flow" of metals. 



Professor Thurston, who, nearly simultaneously with Com- 

 mander L. A. Beardslee, ascertained that an increased power 

 of resisting stress was developed in iron and steel by their sub- 

 jection to a strain which produced distortion beyond the elas- 

 tic limit, and gave them a set, has lately presented a paper to 

 the American Society of Civil Engineers, in which he has given 

 the results of extended researches as applied to other metals. 

 He concludes that the simple extension or straining of any 

 member of any metallic structure is not a cause of weakness 

 except where it produces an actual reduction of section resist- 

 ing rupture, or where it brings the line of stress into a new di- 

 rection, in which it acts either with a larger component of force 

 in the former direction of stress, or, as in the case of a reflexure 

 of the metal, it takes the material at disadvantag:e stratesret- 

 ically after a new disposition of its particles has taken place. 



The conclusion seems also proper that the elevation of the 

 elastic limit by strain can only occur in metals which are elastic, 

 and are capable of being placed in a condition of reduced resist- 

 ing power by internal stress, by artificial or external force. 



Finally, the conclusion has been arrived at that structures 

 fire not weakened by stresses exceeding the elastic power of 

 their members, whatever the material of which they are com- 

 posed, and even when made of metals having no elasticity, and 

 capable of yielding, like tin, by flow, unless such strains as are 

 produced are productive of actual molecular disruption. 

 Letter of JR. II. Thurston. 



THE PLASTICITY OF ICE. 



Professor Dr. Pfaff has communicated to the Physical So- 

 ciety at Erlangen some experiments upon the plasticity of ice, 

 his experiments being made with the object of obtaining some 

 exact numerical data as to the pressure necessary to change 

 the form of a mass of ice, since it is essentially interesting in 

 the theory of glacial movements to determine the minimum 

 pressure at which the ice is plastic. He finds that even the 

 lightest pressure is sufficient to make one particle of ice slide 

 from another, if it only acts constantly and at a temperature 

 near the melting-point; that, in fact, near the melting-point 

 ice behaves like wax. The results obtained by him com- 



