Constanta of Solid Bodies. 271 



forated by holes ; otherwise the tenacity of a piece of gold leaf 

 must be greater than experiment shows to be the case. If we 

 take care that these holes are wanting, or are present in small 

 quantity, the tenacity is very great. The author has deposited 

 thin layers of platinum, silver, or gold upon plane glass surfaces, 

 and is astounded at the tenacity possessed by layers of O'Ol mil- 

 lim. thickness. A suitably formed piece of steel planes regular 

 shavings in such a layer. Copper deposited upon the silver layer 

 gives, together with the silver, a very firm membrane. On tear- 

 ing from the glass, the side turned towards the glass is convex, 

 the other is concave. The author thinks it probable that it is 

 chiefly the tension on the free metallic surface (which, according 

 to theory, must be greater than at the limit of glass) that pro- 

 duces this curvature. Hence a metal with a high capillarity- 

 constant, like platinum, does not adhere to glass surfaces when 

 it is deposited upon them in the cold, but acquires cracks and 

 peels off. It is only after the tension on the surface has been 

 diminished by strong heating that the metal adheres more firmly. 

 If by the pressure of polishing the density and therewith the 

 capillary tension of the metallic surface are increased, metallic 

 layers become detached from the glass, which would otherwise 

 adhere firmly. Measurements of the tenacity of such thin layers 

 were not made by the author, owing to the difficulty of fastening 

 and loading them. 



If thin metallic laminse like gold leaf be raised to a higher 

 temperature, by which the mobility of the individual particles is 

 increased, they curve in consequence of the superficial tension 

 (just as liquid drops form from a thin layer of liquid), and the 

 pores of the thin metallic laminse become larger. This explains 

 the phenomena observed by Faraday in thin metallic lamina?*. 



The principle adduced above, that in the common surface of 

 two solids there is a capillary tension, renders it possible to 

 foresee the explanation of a few other known but hitherto unex- 

 plained phenomena. 



Two plates adhere more firmly the thinner the layer of liquid 

 between them. In like manner, two solids stick the more closely 

 the thinner the layer of cement or glue between them. 



The tenacity of damask steel or rolled iron depends on the 

 circumstance that in the manufacture care is taken to produce a 

 great capillar3 r -surface — the junction of heterogeneous substances. 

 Different kinds of iron are packed over each other and joined 

 by rolling and welding; it is not improbable that they remain 

 separated by an extremely thin layer of oxide or of slag. Heated 

 afresh between each welding, the soft masses may arrange their 



* Phil. Trans. 1847, p. 145. Faraday, 'Experimental Researches,' 

 vol. iv. pp. 401 et seq. 



