264 Mr. G. T, Beilby on the Hard 
have attempted to indicate on a very large scale the steps in 
the hardening process from the surface inwards. Fig. 1 is a 
vertical section across a surface at which two er ystals of 
different orientation meet. Fig. 2 shows the same after the 
surface has been flowed to a considerable depth. 
Fig. 2 
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cig micrographs illustr re surface- flow in gold, silver, 
copper, lead, antimony, &ec., have already been “published ; 
but some of these are reproduced here for convenient reference 
(figs 9-20). 
Figs. 3-8 show the vitreous surface, the granular under 
surface, and the distorted grains in a specimen annealed, 
beaten, ‘and then slightly etched in two stages. The evidence 
afforded by the micro-structure is further discussed in pars. 39, 
40, 49, 50, 61, 68, and 71. 
Optical Properties of Hardened and Annealed Silver. 
29. Even in its moderately attenuated forms, such as 
beaten leaves and films deposited by chemical means on glass 
or mica, silver in its hardened state is highly reflecting and 
only slightly translucent. By heating to from 250° to 300° 
the leaf or film becomes transparent, and loses much of its 
reflecting quality. 
By flowing or burnishing the annealed leaf or film its 
opacity and reflecting-power are restored. 
These remarkable effects were first observed by Faraday, 
who concluded that in the two states the metal was in two 
perfectly distinct forms *. My own observations have con- 
firmed and extended the results obtained by Faraday fT. 
* Faraday’s ‘ Researches in Chemistry and Physics,’ pp. 398-399. 
+ Proc. Roy. Soe. vol. xxii. pp. 226-227. 
