250 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
The blast-pipe and hollow piston-rod, s, bears the piston head, a, in the 
cylinder, v. A handle, u, is formed on the pipe, and others, h, on the cylin- 
der. The ends, h' h", of the cylinder should be convex or concave to give 
stiffness to the sheet metal of which they in this instance are formed. 
Also at the end, h', the piston-head, a, is prevented by the convexity 
from approaching too close to the piston rod passage or its packing at 
the neck of the cylinder, thus tending to keep the piston parallel with 
the cylinder or prevent its rocking in the same. The sides of the cyl- 
inder are preferably double, in order that bruises of the outer wall 
may not, affect the smoothness of the inner wall, and for other purposes. 
The valves are of the kind described for my bellows heads above. 
These incurrent valves are made near the ends of the cylinder, at oo, 
and they act in alternation. 
The piston-head has flexible margins, which hug the cylinder loosely, 
but more tightly under the air pressure. To make these margins a belt 
of flexible material, broader than the head, a, has its center shrunk by 
a tight wire into a groove in the circumference of the head, or a pair 
of flexible cups may be used joined base to base. The head is free to 
slide on the piston-rod for a very short space between the two annular 
flanges or beartngs, which may be alternately applied to their packings 
on the head. These packings could be free or attached to the flanges. 
It may be observed that when the head is against the one flange there 
is left open an entrance between the head and the other flange as an 
inlet from one end of the cylinder into the piston-rod aud blast pas- 
sage 5 also that when the head is against the other flange said entrance 
is shut off from that end of the cylinder, and there is uncovered another 
opening at the opposite side of the head as an outlet from the other end 
of the cylinder into the hollow piston and blast-pipe. When either the 
cylinder or the piston rod is moved reciprocatingly with reference to 
the other the pipe inlets are alternately opened and closed, the slip- 
head of the piston acting as a valve in opposition to the end valves, so 
that both strokes of the piston or cylinder discharge the blast, making 
it constant. A piston-rod with a single inlet may be used, so placed 
that the slip causes it to appear first on one side of the head and then 
on the other. The pump is calculated to be worked by the two hands, 
one hand at u, holding the piston or blast-pipe, while the other hand 
at h moves the cylinder, v, back and forth. Where this sort of pump 
is combined in machines any method of giving reciprocating motion in 
such machines will answer for operating it. 
In this connection it may be well to state that Mr. Henry Hunphro- 
Wile, of Mountville, Pa., patented in 1880, 1881, and 1882, (No. 251886), 
some air-pumps for spray-dampeners, the latter being very simple, but 
not specially adapted for spraying upon plants, since only the oid-faftb- 
ioned atomizing principle is used, and not in such shape as to discharge 
upward, There are many air-pumps in the market, but such as are 
specially needed lor held use have not yet appeared in the trade. That 
