fig. 8), which, however, is exaggerated to give a clearer idea of the
actual movements, which are on quite a small scale. The line AB
represents the bottom of the trough, while CC are two of the spring
legs; the full lines indicate the spring legs at the extreme backward
position of the crank, while the dotted lines show the spring legs and
bottom of the trough at the extreme forward position of the crank D.
The material to be conveyed, represented by E, is thrown forward by
the forward movement of the crank, and describes a short parabolic
curve; it is thrown at about a right angle to the inclined legs CC,
but before it has time to complete its parabolic course, the trough
has been moved by the crank into its original position. As soon as the
material has dropped down, the trough makes another forward movement,
whereupon the material is thrown forward another stage, and this
process, which is continually repeated, as indicated by the letters
E1, E2, E3, has the effect of carrying or conveying the material in
the direction desired. It is important to note that the actual
movement both of trough and material is within narrow bounds; the
horizontal movement of the trough is only about 1 in., while the
vertical or upward movement is about 1/8 in. The material is conveyed
by this vibrating trough with a minimum of friction, as it is evident
that the material is carried forward without any contact with the
trough, while the very nature of the motion precludes injurious
friction between the particles themselves. When the trough is full the
material will move as it were in a solid mass.

An important improvement in this type of vibrating trough conveyor is
the balanced conveyor, in which the trough is made in two sections,
one being placed at a slightly lower level than the other, so that
one-half may deliver into the other half. The two sections are driven
by triple or quadruple cranks set at an angle of about 180 deg. to one
another. In this case one-half of the conveyor will move forward while
the other moves backward, thus balancing each other (fig. 9). At the
same time the material keeps moving in the same direction because all
the spring legs are of the same inclination. It is usual to drive
balanced conveyors at or near the centre of their length, but they may
also be driven from one end, in which case the balancing of the
conveyor would be effected by