SEA SAND. 
49 
Galton in his “ Natural Inheritance,” has used this curve to 
study the problems of heredity; and for this and other work 
the Royal Society has just awarded the Darwin medal to him. 
Dr. Russell Wallace has suggested, and Prof= Karl Pearson 
has greatly developed the use of the curve for the exact study 
of variation in animals and plants. But we must leave the 
further discussion of this to the York Naturalists. 
For us the curve indicates the proportions between sand 
particles of different grades which will be deposited side by 
side. If you like, it indicates the error in the water deposition 
method of attempting to sort sand into different sizes. The 
grains differ in shape, in size, in density, and these small 
differences must affect and may combine to equalize their 
rates of fall. The history of any single grain is a long chapter 
of accidents, that is of causes which defy our powers ol 
analysis. 
The long chain of causes which brought certain grains of 
sand into the laboratory is as intricate as that other chain of 
causes which brought together certain people to consider its 
properties. Trace back the individual life histories of the 
inquirers and their family histories for a thousand generations, 
and consider what innumerable causes have conspired to con¬ 
centrate them into one room. The curve described above stands 
for the law of error, the rule of accidents, the order in chaos. 
The mathematical theory of it is worked out on the hypothesis 
of an infinite of infinitesimal causes all equally probable. 
The word calculus once meant a pebble : now it applies to 
a branch of mathematics in which the pebbles are ground finer 
than the finest sand, though the total of sand is still equal to 
the pebbles from which it was made. 
But if we submit our sand to any new series of accidents we 
shall get a result of the same form, provided the causes are 
very many, equal in magnitude and equally probable. For 
instance, if a stream of fine sand is allowed to fall on a series 
of horizontal sheets of wire gauze placed one above the other, 
each grain as it strikes the wires may be turned just in or just 
out of the meshes, or bouncing may be thrown still further 
out. The first grains that fall are laid out like bullet marks 
on a target, most numerous near the middle, fewer towards 
