1910] on Electrical and other Properties of Sand. li:l 



the pressure of the foot disturbs the arrangement of the sand -particles 

 from one of normal piling to one in which the interstices between 

 the grains become larger. Since these spaces were originally full of 

 water (held up by capillarity) they are now no longer filled, and we 

 obtain a comparatively dry area. Water is rapidly drawn in from all 

 sides, however, by the partial vacuum formed in the interstices, and the 

 internal friction diminishes. The sand feels insecure. On withdraw- 

 ing the foot normal piling is resumed, the excess of water producing 

 a puddle, until it slowly percolates away whence it came. 



This brings me to the subject of quicksands. 



A certain amount of unnecessary mystery seems to surround this 

 matter. J hasten to point out that the grains of quicksands appear 

 to be in no way extraordinary. Nevertheless the fact remains, that 

 sand in certain localities upon the coast readily gives way under a load. 

 Instances are recorded where a cart driven over a wet shore has rapidly 

 disappeared below the surface. The general opinion seems to be that 

 this is due to a soft underlying layer of clay or mud, which no doubt 

 in some instances is the true explanation. Mr. Carus- Wilson, who is 

 an expert in these matters, pointed out to me recently, however, that 

 another factor may be the imprisoning of gas between the grains, due 

 to decomposition of organic matter. Experiment certainly supports 

 this view, for you see that one of these beakers of wet sand easily 

 sustains a weight which sinks down in the other. Yet both appear 

 similar. The sand in the second beaker, however, was mixed when 

 dry with a powder capable of effervescing if wetted. In the neigh- 

 bourhood of dangerous bogs, in Ireland especially, it is evident that a 

 quantity of gas is imprisoned in the mud. 



It must also be borne in mind, that any surface in so good a contact 

 with wet sand that the air is excluded will be held fast by atmo- 

 spheric pressure. And further, that an object so situated and tilted 

 this way and that will rapidly become embedded and swallowed up. 

 It is by this simple process that the celebrated Goodwin Sands 

 have claimed so many victims. A large percentage of the vessels 

 stranded upon them, however, float safely off on the rising tide, but 

 now and then one is caught and doomed. In the past they have been 

 responsible for many a shipping tragedy, and there is a pathetic interest 

 attaching to the fact that ribs and other remains of ships, long lost 

 and forgotten, sometimes re-appear for a time above the surface. 



Since the advent of steam it is happily a rare occurrence for a 

 vessel to be lost upon a sandbank. 



In 1849 boring operations were carried out on the Goodwins by 

 the engineering staff of Trinity House. 



The Deputy Master and Brethren, whose generous offer of assist- 

 ance on all matters relating to this subject I gratefully acknowledge, 

 have kindly lent a model made at the time, which shows the nature 

 of the sand found at increasing depths. Solid chalk was reached at 

 80 feet below the surface. 



