242 The Evolution of Agricultural Implements. 
of chaff and in the rotary corn-screens, first introduced by Penny 
in 1860, for cleaning and sizing grain. Since the expirj’ of 
Underhill’s patent, in 1873, the use of a separate exhaust fan 
for bagging chaff has become general, while in 1881, Foden, of 
Sandbach, patented a method for making one exhaust fan do the 
whole work of a threshing-machine, and with such a thresher 
the same maker took the first prize at the Society’s recent ti’ials 
at Doncaster in 1891. 
In 1876, Walworth and Co., of Bradford, introduced a 
simple machine for cleaning grain, in which riddles are entirely 
dispensed with and separation is effected by means of gravity 
alone. In this dresser, com, falling through an exhausted 
chamber, is arrested six times in succession by as many inclined 
wooden shelves, beneath each of which air rushes into the 
partial vacuum created by the fan. The grain is thus many 
times weighed, so to speak, in a delicate air balance, and the 
resulting samples are each composed of grains of exactly the 
same specific gravity. 
Class V. — Machines for Preparing Crops for Food. 
Gnnding Mills . — Although not, strictly speaking, agricul- 
tural machines, corn mills cannot properly be excluded from 
this paper without remark, all the more imperatively demanded 
because milling, perhaps the oldest of all mechanical processes, 
is just now undergoing something very like a revolution. For 
several years past the English miller has found himself in- 
creasingly unable to compete with his Hungarian and American 
rivals in the production of the finer qualities of flour, and 
his eyes have been recently opened to the fact that he must 
either adopt new methods of grinding or be beaten by his foreign 
competitors. 
“ Roller milling,” — under some form of which process the 
countries in question have obtained their commanding position 
in the markets for fine flour, — came into use in the following 
way. Hungarian and American wheats have extremely thin, 
brittle skins, which, when ground in the ordinary manner, are 
broken up into the finest particles, and, passing through the 
dressing-machine with the meal, give the latter a dark colour, 
greatly diminishing its commercial value. Where, as in England, 
wheat has a tough skin, “ low gi’inding ” under millstones gives 
satisfactory results, the bran becoming flattened into flakes, 
easily separable from the flour, and themselves commercially 
valuable by reason of their large size. But, probably, two-thirds 
of the grain now ground in Great Britain is of foreign growth. 
