224 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
circumference on the ascending side. The objection to feeding at the 
center is that, on account of gravitation, the spray is thrown more down- 
ward than upward, whereas the ascending side entirely opposes gravita- 
tion, and throws off the material before it is carried around to where 
gravity can pull it off downward. 
If the brush be rotated in a cylindrical trough supplied with the 
fluid, the latter is dipped out and thrown in too great volumes, unless 
the quantity in the trough be kept at just such depth that too much 
cannot be caught and lifted. To keep thus a constant shallow sup- 
ply in the trough it may be fed by the automatic drip process, such as 
is employed in automatic inkstands, &c. A tube from an air-tight 
liquid reservoir descends into the trough near to its bottom. The 
height of this drip orifice gauges the depth of the liquid ; for when enough 
flows to submerge this outlet air cannot enter it to press the liquid out, 
and only after the brush has thrown out enough to lower it can more 
air enter and the liquid again flow to the same level. 
This process is a little more difficult and complicated than the free 
drip method, in which the trough may or may not be used. In the latter 
method the amount thrown is gauged by the size of the smallest caliber 
of the feed spout. 
Brushes may also be used as feeders or throwers of powder. They 
may be used on sifters, to keep their small passages open and help rattle 
the powder through them. Also a brush may be worked in a powder 
reservoir or hopper to feed out the powder upon plants or into a blast 
from a blower, to be swept thereby to the substances being injured by 
insects. 
These brushes will throw powder to some distance and in an excel- 
lently diffused cloud, but quite fine powder, like flour, &c, cannot be 
thrown very far through the air, because the particles are so small as 
to have little momentum, and soon become stopped by the resistance of 
the atmosphere; but coarser powders, like corn meal, sand, &c, are 
thrown a much greater distance by the same force. Yet in either case 
much more distance ean be attained by encasing the rotary brush, or 
reel, or wheel, in such a manner that it may act as a blower, and throw 
a blast of air along with the powder. The stronger the blast the farther 
the powder will be thrown, and the coarser the powder the sooner will 
it fall. In these respects it is seen that the thrower-discharge is the 
opposite of the blower-discharge. 
Some machines involving the use of brushes need to be noticed here. 
Plate XXVII, Fig. 1, represents in plan section a brush-machine of sim- 
ple construction, and illustrates a method of encasing rotary brushes to be 
fed by powder or liquid, and in order to throw the same by the elasticity 
of their bristles springing from beneath a surface against which they 
are revolved. 
The cylindriform brush d, turns (in the direction indicated by the 
arrow) in a trough open on the side, and bears the square powder-can, 
