224 Mr. G. T. Beilby. Surfw,- Fh<- in (.'ft/f//i,ic [May 23, 



A thin field of magnesium oxide was obtained by holding a glass 

 slip over burning magnesium. Films of any degree of thickness 

 may be readily obtained in this way. The film selected was trans- 

 lucent, and was bluish- white by reflected light. The rounded end of 

 an agate pestle was lightly pressed on the film and slightly rolled 

 upon it. As the film adhered more and more firmly to the glass, the 

 pressure was increased. The experiment is not always successful, as 

 the film of oxide sometimes sticks to the pestle instead of to the 

 glass, but with a little care it is easy to obtain flowed or welded 

 patches of magnesium oxide. These patches are smooth and trans- 

 parent, like glass ; their structure will be referred to again in another 

 connection. 



In beating or planishing metal on a smooth surface, the flow is not 

 so strictly confined to the surface nor to the exact spot at which the 

 pressure is applied, as it is in the case of hard, brittle substances. In 

 the softer metals the flow proceeds much further from the centre 

 of pressure than it does in the harder. Very minute crystalline 

 fragments of antimony or bismuth can be beaten into scales, and their 

 flow appears to be as perfect as that of gold or silver. As the size of 

 the particles is increased, the outer edge of the minute plates 

 developes notches and radial cracks, showing that the limits of flow 

 liave been exceeded. 



It appears not unlikely than an accurate method of comparing 

 the hardness and malleability of metals might be based on the 

 behaviour of minute particles during their flow under uniform con- 

 ditions of pressure. 



DESCRIPTION OF PLATES 9 AND 10. 



PLATE 9. 



Fig. 1. Iceland spar showing etched and unetched surface. 



Light, transmitted slightly oblique, green screen. 



Objective 16 rnm. Apochromat. N.A. 0'3. x 215. 

 Fig. 2. Crystalline antimony after rubbing on fine emery paper. 



Light, normal reflected, green screen. 



Objective 3 mm. Oil immersion. Apochromat. X.A. 1'4. x 775. 

 Fig. 3. The same after polishing on rouged leather. 



Light and objective as in fig. 2. x 775. 



Fig. 4. The same after partial etching with KCy. 

 Light and objective as in fig. 2. x 775. 



Fig. 5. The same showing pits covered with film of flowed metal. 

 Light and objective as in fig. 2. x 775. 



Fig. 6. The same showing another pit over which a film is being built up by the 



flowing metal. 

 Light and objective as in fig. 2. x 775. 



All of . the above are from direct photographs without enlargement orjreduction. 



