n on the cut, but are on the exterior
case removed to show the construction.

[Illustration: Fig. 59.]

[Illustration: Fig. 60.]

Fig. 60 is an elevation of a boiler with Clark's Patent Steam and Fire
Regulator attached, for the control of the draft of the chimney by the
pressure of steam in the boiler. It consists of a chamber, _a_, with a
flexible diaphragm or cover on top, in communication with the boiler. On
this diaphragm rests a plunger or piston, which is held down like a safety
valve, by a lever and weight, _b_. The end of the lever is connected with a
balanced damper, _c_, in the chimney. The weight, _b_, is placed at any
required position on the lever, and when the pressure of steam in the
boiler, exerted on the diaphragm, becomes sufficient to raise the weight,
the lever rises, and the damper begins to close, and to check the draft in
the chimney. When properly adjusted, the machine works on a variation of
from, one to two pounds between the extremes of motion. When the dampers
are very large, say 3 feet or over, they should be set on rollers, like
common grindstone rollers; the regulator should be attached directly to the
damper, the length of the pipe connecting the regulator with the boiler
being of no account.

[Illustration: Fig. 61.]

Porter's Patent Governor, fig. 61, is a modification of the ordinary
centrifugal governor. Very small balls are employed, from 2-1/4 to 2-5/8
inches in diameter. These swing from a single joint at the axis of the
spindle, which is the most sensitive arrangement, and make from 300 to 350
revolutions per minute, at which speed their centrifugal force lifts the
counterpoise. The lower arms are jointed to the upper ones at the centres
of the balls, and connect with the slide by joints about two inches apart.
The counterpoise may be attached to the slide in any manner; for the sake
of elegance, it is put in the form of a vase rising between the arms, its
stem forming the slide. The vase is hollow and filled with lead, and weighs
from 60 lbs. to 175 lbs. It moves freely on the spindle, through nearly
twice the vertical distances traversed by the balls, and is capable of
rising from 2-1/2 to 3 inches, before its rim will touch the arms. It is
represented in the figure as lifted through about one half of its range of
action.

The standard is bored out of the solid, forming a long and perfect bearing
for the spindle; the arms and balls are of gun metal, the joint pins of
ste