1903.] Solids under Mechanical Disturbance. 223 



The experiments with antimony show the same phenomena in a 

 much rougher way, and in that case we gain a slight clue to the 

 mechanism by which the flow is produced. Beginning at the rougher 

 end of the polishing process, we can see that the projecting points of 

 the file plough their way through the metal carrying with them a 

 certain proportion of it, but also leaving behind in the furrows and on 

 the ridges a smooth covering film of metal, which has flowed at the 

 moment when tlie moving point with its burden of accumulated metal 

 passed over it. With the emery grains the same operation is repeated, 

 but in their case there is less ploughing action, and the proportion of 

 the metal which adheres to the polishing agent is much greater 

 and the flowing action is more pronounced. When the rouge stage 

 is reached there appears to be no cutting or ploughing action to 

 speak of, the particles of rouge seem to have the power of seizing the 

 surface so as to set the molecules gliding without actually removing 

 much metal. As the molecules or molecular aggregates glide over 

 each other within the range of their molecular forces, the conditions of 

 the liquid state are to a considerable extent fulfilled and the forms 

 assumed by the surface are determined, as in a viscous liquid, by surface 

 tension. This view will be more fully discussed in connection with 

 observations on " The Effect of Heat on Thin Films and Surface 

 Layers " and on " The Aggregation of Solids under the Influence of the 

 Molecular Forces " which will be detailed in Parts II and III of this 

 paper. Whether the minute elements which are made to glide over 

 each other in a state of comparative freedom are individual molecules, 

 or whether they are aggregates of molecules is still an open question ; 

 but numerous observations have been collected which may throw light 

 on the matter. These it is proposed to present in Part IV of this paper 

 on " Granular and Spicular Structure and the Transparence of Metals." 



In a previous communication, various experiments were described 

 which showed that glass and other silicates in a finely divided state 

 can be welded together into larger masses by pressure. In this way a 

 mass of thin films of blown glass was pressed into a compact layer. 

 In grinding glass in an agate mortar it was found that the rolling under 

 the pestle tended to aggregate the finer particles into granular masses. 



In recent experiments with calc-spar it has been found that the 

 appearance of surface flow can be produced by pressure. One of the 

 faces of a crystal of Iceland spar was rubbed, first on a fine file and 

 then on the emery block till a fine grained surface was produced. By 

 strongly pressing the roughened face on a smooth, hard, slightly 

 convex surface, little patches of flow were developed. These patches 

 were perfectly distinct from the roughened surface by which they were 

 surrounded, and their boundaries were well defined and flowing like 

 those of a drop of liquid pressed between two plates of glass. The 

 surface of these patches had the perfect smoothness of a liquid surface. 



