MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
391 
of a light board, on which weights ma}^ be placed. A fairly uniform pressure may thus 
be maintained for a considerable time when the jet is small. 
For the preparation of the jet orifice a wide tube of fusible glass is selected, free 
from lead and of uniform thickness ; this is carefully heated at one point with constant 
rotation, and drawn out. The constricted, portion is then cut with a sharp file where 
it has the desired internal diameter, the edges of the orifice carefully ground off on a 
stone and finally slightly fused. 
To facilitate the adjustment of the hearing-tube or flame, some form of apparatus like 
the following is desirable (fig. 3). On a wooden base, A A', about 12 inches long by 
4 inches broad, a vertical block B is mounted. The glass jet-tube J rests in a groove 
Fig. 3. 
on the top of B, and is held in position by two spring clips, c c. The hearing tube, T, 
is a brass tube about ^ of an inch in internal diameter, on the end of which nozzles, 
N, having orifices of different sizes, may be screwed. T is held in position by two 
stout clips, d cl', on a brass plate, e e, about 2 inches long by f of an inch wide, which 
is pivoted at e' on another brass plate, f f, of nearly the same length but about 
2 inches wide. A stout spring, s, presses the little plate e e' firmly against the point of 
the screw q, which plays in a block on the plate f f. The plate f f is hinged at one 
end to the similar plate g g ', soldered obliquely on the top of a brass pillar, P, which 
slides easily in the tube Z, and may be clamped in any position by the screw O. The 
tube Z is soldered to a brass plate, s s', which may be screwed to the base board. A 
stout screw, Q, plays through the plate g g', and the plate f f is firmly drawn down 
against its point by a spiral spring, not shown in the figure. Thus, by sliding P in the 
tube Z, the orifice may be brought approximately into position ; after which a finer 
