124 SUMMARY OF CURRENT RESEARCHES RELATING TO 



area of the field in square centimetres is — — ; hence the area occupied 



by the mineral can be estimated as a percentage of the area of the field. 

 This is done for several fields, and an average taken. In most cases 

 this method is quite accurate, but in exceptional instances, e.g. where 

 mica plates appear edge-on in the field, certain allowances mnst be made, 

 otherwise the quantity of the constituent would b2 underestimated. 



Microscopic Study of the Prehistoric Bronzes of the Charente.* 

 M. G. Chesneau has microscopically examined the metal of two pre- 

 historic bronze axe-heads. One head was provided with a socket ; the 

 other merely heeled. It is admitted that the former is the more recent 

 type of weapon. Micrographic analysis reveals that, at any rate in the 

 Charente district, axes were used rough from the mould at the beginning 

 of the Bronze Age, but that later on the methods of manufacture were 

 improved, and the axe, after casting, was submitted to numerous re- 

 heatings and hammerings at high temperatures to increase the hardness 

 of the material. 



Surface Structure of Solids.f — G. T. Beilby seems to succeed in 

 proving the following important propositions by means of his series of 

 photomicrographs of metallic films : 



(1) The operations of cutting, filing, grinding or polishing, produce 

 on the surface of solids a thin film, which is in many respects essentially 

 different to the general body underneath it. 



(2) This surface film results from a certain mobility, which is con- 

 ferred on a thin layer of molecules by the tool or polishing agent 

 moving over the surface. 



(3) While it is in the mobile condition, the film of solid molecules 

 behaves like a liquid, and is subject to the action of surface tension. 



(4) If these propositions are established it will follow that a truly 

 polished surface is one in which, for a certain minute depth, the sub- 

 stance has been liquefied and then smoothed by the action of surface 

 tension. 



(5) Heat and solvents can confer on the molecules of solids sufficient 

 mobility to enable their films or other minute portions of the solid to 

 behave like a liquid. 



(6) In the aggregation of solids from their molecules there is a 

 certain size of the aggregate up to which its form is controlled by 

 surface tension, and only after this point is passed can crystallic force 

 come into play. 



(7) The metals are the most opaque bodies we know, but their 

 substance is nevertheless intrinsically transparent. 



(8) The " spicular " appearance frequently to be seen by the Micro- 

 scope on the surface of metals, and other solids under obliquely- 

 reflected light is due to a granular texture in the thin translucent film 

 with which the surface is covered. 



(9) This granular texture results wholly or in part from the action 

 of surface tension on the surface layer of molecules, while it is in the 

 mobile condition. 



* Comples Rendus, cxxxvii. (1903) pp. 930-2 (2 figs.). 



f Third Hunter Memorial Leeturo, G! isj^ow, 1903, 55 pp., 42 pliotomicros. 



