1910] on Electrical and other Projferties of Sand. 743 



this subject, has clearly proved, however, that the formation of a sand 

 dune is very frequently due to wind eddies. The second photograph 

 upon the screen was, in fact, taken by him in Egypt, and depicts 

 the steady irresistible march of millions of tons of sand, encroaching 

 upon and slowly burying casuarina trees. (Fig. 2.) 



To come nearer home, the seriousness of problems arising out of 

 this state of things may be illustrated by two photographs obtained 

 recently at Southport in Lancashire. 



In the first one (Fig. o), the back garden of a newly built house 

 is nearly buried beneath the enormous hill which will probably soon 

 cover the whole property. Tlie second slide (Fig. 4) shows that 

 the familiar appearance of a sandy beach at low water, with regular 

 lines of ripples, may be produced by the direct action of the wind, 

 and, incidentally, the utter futility of constructing an esplanade in 

 such a neighbourhood. All these phenomena depend, in some 

 measure, upon the size, weight and shape of the sand grains 

 themselves. 



Silica, a substance which occurs in numerous impure forms and 

 constitutes a large portion of the rock masses known to geologists, is 

 also, to be found in a pure state as crystalline quartz. Here is an 

 actual specimen about IS inches long, which together with the 

 beautiful group of quartz crystals by its side, known as amethysts 

 (and tinted probably by a trace of organic matter), are the property 

 of this Institution. Sand, therefore, being the result of rock dis- 

 integration assisted by the grinding action due to the motion of wind 

 or water, varies in composition in diif erent localities. 



The next slides are micro-photographs taken with a low-power 

 objective. 



They represent some grains of sand found at Charlton and the 

 Isle of Eigg respectively. (Figs. 5 and 6.) 



The former are seen to consist of minute silica particles of very 

 irregular form, whereas the larger grains of the Eigg sand are 

 remarkable for their smoothness. It is owing to this fact that the 

 latter possess a peculiar property to be referred to later. 



Owing to the Sahara Desert having once formed the bed of 

 a vast sea, it is of course found to be rich in marine deposit. 



The damage which sand is capable of doing has been already 

 referred to. It must not be forgotten, however, that its utility in 

 the arts and crafts is of the utmost importance. 



The Egyptians are reputed to have been the first to find a wide 

 use for it. They were probably the earliest glass-workers in the 

 world. 



By the time glass making was begun in England, viz. about 1611, 

 the Romans and Venetians had so far mastered the art of blending 

 sand with other substances, that almost all the technical difficulties 

 had akeady been overcome. 



Now the melting point of silica being about oOOU" C, it cannot 



