﻿172 DE. H. C. SORBY OX THE APPLICATIOX OF [^^T I908, 



whicli cannot be explained in a satisfactory manner. Notwith- 

 standing this, it appears desirable to do the best that I can with 

 the material at my disposal, hoping to lead others to do what I 

 intended to do, and correct such errors as are now unavoidable. 



In order to clear the way tor subsequent detail, I describe a few 

 general facts. To learn the final velocities of subsiding sediment 

 I made many experiments, and found it a most complex question, 

 requiring much more study. Coarse and somewhat fine sand-grains 

 subside and collect at once on the bottom in a fairly-settled con- 

 dition, yet the interspaces between the grains may amount to half 

 the total bulk. Very fine-grained material, when more than 1 per 

 cent, of the water, behaves in a totally-different manner, and, as a 

 whole, somewhat like an imperfect liquid ; and, in extreme cases, 

 even after standing for a year, it may contain 9u per cent, of 

 water. Very fine-grained sand possesses this latter property to a 

 slight extent. 



II. FiXAL Velocities. 



In the year 1859 I made many experiments, in order to learn the 

 laws regulating the subsidence of various solid substances in 

 water, more especially of sand and flakes of mica. Their size was 

 first carefully measured with a micrometer-microscope, and those 

 were selected which were of fairly-uniform diameter in all directions, 

 but only the smallest were adojDted for the calculations. These 

 grains were carefully introduced separately in a wet condition into 

 a tall jar of water, and the number of seconds which they occupied 

 in subsiding a foot and a halt was observed. In experimenting 

 with spheres, cubes, and thin plates of glass, as well as with grains 

 of sand and mica, it was found that the relation between the final 

 velocity and the diameter is of so complex a character that it 

 cannot be expressed in any simple manner, as though the result 

 depends on complex conditions. I therefore fall back on experi- 

 ment, and deal only with such cases as are of geological interest ; 

 but I may say that spheres, cubes, and plates of glass yield similar 

 results. 



Grains of Sand. 



My best experiments were with grains varying from 1 to 

 inch in diameter, which gave final velocities from about a foot 



1 



200 



down to -055 foot per second. For diameters varying from two- 

 fifths to a fifth of an inch, the final velocity was found to agree 

 well with the supposition that it varies as the square root of the 

 diameter. When the diameter is about a tenth of an inch this law 

 gives too large a result, but when it is about a fiftieth of an inch 

 this excess increases, and when the diameter is about a hundredth 

 of an inch the final velocity is only half what it would be if 

 the same law holds true for the small grains as for the large. In 

 fact, for grains measuring a hundredth of an inch in diameter and 

 somewhat less, the final velocity varies nearly as the diameter. 

 It seems ta me probable that these facts may be explained by 



