178 REPORT—1863. 
Richards’s Jndicator for Steam Engines, By C. T. Portsr. 
This instrument (invented by Mr. Charles B. Richards, an engineer of Hartford, 
Connecticut, U. 8.) is constructed on a plan by which it is found that the errors in 
the motion of the paper and those in the motion of the pencil are quite avoided, 
and correct diagrams are obtained under all circumstances. The principal dis- 
tinguishing features of this instrument are a short and strong spring, a short mo- 
tion of piston, and light reciprocating parts, combined with a considerable area of 
cylinder, and an arrangement of levers and a parallel motion for multiplying the 
motion of the piston in such a manner that the diagram is described in the usual 
way and of the ordinary size. The proportion between the motion of the piston 
and that of the pencil is a matter of discretion; that which has been adopted is 
1 to 4, and the steadiness with which the indication is drawn by these instruments, 
even at the highest speeds of piston, leaves nothing to be desired. 
In respect to the ability of these indicators to give diagrams which shall be per- 
fectly accurate, it is to be observed that the spring moves without any tendency to 
bend, and the motion of the piston, and the length of cylinder to be filled with 
steam as the piston rises, are one-fourth of those in the ordinary indicator. It is 
assumed, also, that if the motion could be frictionless, then the approach to simul- 
taneousness in the action of an indicator would be in a direct ratio to the strength 
of the counteracting forces, existing in the pressure of the steam on the one side of 
the piston and the resistance of the spring on the other, and in an inverse ratio to 
the distance through which the piston has to move upon any given disturbance of 
their equilibrium. But, moreover, the motion cannot be absolutely frictionless ; and 
if the friction should be equal in two indicators of different strokes, then the resist- 
ance from it, in each one, would be in proportion to the length of its stroke ; and if 
the resistance from friction should be equal in two indicators having different areas 
of piston, then its effect on the diagrams given by them would be in an inverse 
ratio to the areas of the pistons. In every view which can be taken, it is evident 
that the features embodied in this indicator—namely, a strong spring, short motion 
of piston, and light moving of parts, combined with a reasonably large area of 
cylinder—are essential for the attainment of truth in the diagram. 
General Construction of the Indicator.—The parallel motion is made as compact 
as possible. For this purpose, a lever of the third order is employed to multiply 
the motion, and the extremities of the line drawn by the pencil are permitted to 
have a slight curvature, which considerably reduces the length of the rods, and 
does not affect the usefulness of the instrument, the curvature at the lower end 
being below any attainable vacuum, while the extremity of the scale above is very 
rarely employed. 
The indicators are made of a uniform size ; the area of the cylinder is one-half of 
a square inch, its diameter being *7979 of an inch. The piston is not fitted quite 
steam-tight, but is permitted to leak a little; this renders its action more nearly 
frictionless, and does not at all affect the pressure on either side of it. The motion 
of the piston is 3% of an inch, and the motion of the pencil, or extreme height of 
the diagram, is 3} inches. The paper cylinder is 2 inches in diameter; and the 
length of the diagram may be 5} inches, if this extent of motion is given to the 
cord. The diagram is drawn by a pointed brass wire on metallic paper. This isa 
great improvement over the pencil; the point lasts a long time, cannot be broken 
off, and is readily sharpened, and the diagram is indelible. The steam-passage has 
two or three times the area usually given to it. The stem of the indicator is coni- 
cal, and fits in a corresponding seat in the stop-cock, where it is held by a peculiar 
coupling, shown in section in the accompanying woodcut illustration of the indi- 
cator. This arrangement permits the indicator to be turned round, so as to stand 
in any desired position, when, the coupling being turned forward, the difference in 
the pitch of the screws draws the cone firmly into its seat; and when the coupling 
is turned backward, the cone is by the same means started from its seat. The 
leading pulleys may be turned by some pressure, to give any desired direction to 
the cord, and will remain where they are set. By these means the indicator can 
be readily attached in almost any situation: 
- pian 
