The Truth of Grist Mills and Disintegrators at Plymouth. 609 
further will be said either of Blackstone or Lister in this report, 
saving that both these exhibitors showed a well-designed and 
well-made mill, moderate in price, and capable of producing an 
excellent sample of meal, but "out of it," so far as gristing is 
concerned, by large comparative losses of " points of merit " in 
respect of time, power, and adaptability. 
Type II. Flat discs. — Samuel Corbett & Son's grist mill 
(3460), which took the first prize, consists of a pair of grinding 
discs 17^ in. diameter, made of chilled cast-iron, trued on their 
faces by" grinding. The discs have a " dress," illustrated by 
Fig. 2 (Table 2), the & Son , g Firgt pHze QHst mn 
tangential grooves 
being -fa in. pitch 
and \ in. deep at the 
centre, and -f^ in. 
pitch and -Jg- in. deep 
at the periphery of 
the disc. The discs 
are vertically dis- 
posed, and are con- 
tained between the 
bearings of the mill 
spindle, an arrange- 
ment which gives 
great steadiness in 
work. The live disc, 
or " runner," is car- 
ried upon a horizontal 
shaft, driven direct by 
belting at 440 revolu- 
tions per minute, and 
is kept apart from the 
dead disc by means 
of a spiral spring en- 
circling the driving 
shaft, and pressing against the pulley bearing. A set screw, 
acting against the pressure of this spring, adjusts the discs 
for fine or coarse grinding, while an independent pair of 
strong spiral springs, taking the place of Williams's eighteenth- 
century levers, provide for the passage of hard foreign sub- 
stances through the mill without injury to the grinding 
surfaces. The feed consists of a joggling shoot, provided with a 
perforated screen for the separation of straws, sticks, &c. ; while the 
admission of com is regulated by a hopper slide. The joggling 
apparatus in this mill is peculiarly simple and very quiet in 
