1886.] Professor W. CJiaudler Boherts- Austen on Metals, 395 



WEEKLY EVENING MEETING, 



Friday, Marcli 26, 1886. 



Sir William Bowman, Bart. LL.D. F.R.S. Vice-Presideat, in the 



Chair. 



Professor W. Chandler Roberts- Austen, F.R.S. M.B.I, 



CHEMIST OF THE MINT, PROFESSOR OF METALLURGY, NORMAL SCHOOL OF SCIENCE AND 

 ROTAL SCHOOL OF MINES. 



On Certain Properties common to Fluids and Solid Metals, 



In one of the beautiful discourses, delivered in the early part of the last 

 century, which grace the annals of the French Academy of Sciences,* 

 Reaumur observes that industrial art, like nature, has its marvels, 

 which we often fail to notice because they are constantly before us. 



The extraordinary ductility of metals aj)peared to him to involve 

 one of the deepest secrets of nature, and although he held that in 

 his time science was hardly in a position to explain more fully 

 than the old philosophers did, the cause of this property of bodies, 

 it was nevertheless possible to see better than they, what advantage 

 art has gathered from the power of leading and guiding metals by 

 hammering or by traction, and from this point of view, both art and 

 nature seem, he says, to rival each other in furnishing us with 

 remarkable facts. Reaumur then, with singular clearness, defines 

 the conditions under which metals prove to be ductile. The rela- 

 tion between the behaviour of solid metals and fluids has long been 

 recognised, not merely in the sense that atomic motion is common to 

 solids and fluids, and that therefore " everything moves and nothing 

 remains," but apart from theory there is much experimental evidence 

 as to the properties that are common to fluids and solid metals, 

 the characteristics of which, at first sight, seem widely separated. 

 Let me remind you of the elementary definition of the two states, 

 solid and liquid. A solid has a definite external form which either 

 does not change, or only changes with extreme slowness when left 

 to itself, and, in order to change this form rapidly, it is necessary 

 to exert a more or less energetic effort. A liquid, on the other 

 hand, can be said to have no form of its own, as it always assumes 

 that of the containing vessel, the mobility of its particles is extreme, 

 its resistance to rupture is very small, and its free surface is always 

 a plane when the mass is left at rest. Then there is the colloid 

 condition, which intervenes between the liquid and crystalline solid 

 state, extending into both, and probably affecting all kinds of solid 



Histoire de FAcademie Royale des Sciences,' 1713 [vol. for 1739, p. 199]. 



