cylinder and the indicator.

The cylinder of the indicator is fastened upon a wooden or
metal frame, more than twice its own length; one end of a spiral
steel spring, like that of a spring steel-yard, is attached to
the upper part of the frame, and the other end of the spring is
attached to the upper end of the piston-rod of the indicator.
The spring is made of such a strength, that when the cylinder of
the indicator is perfectly exhausted, the pressure of the
atmosphere may force its piston down within an inch of its
bottom. An index being fixed to the top of its piston-rod, the
point where it stands, when quite exhausted, is marked from an
observation of a barometer communicating with the same exhausted
vessel, and the scale divided accordingly.

Improvements come in many ways, sometimes after much thought and after
many experimental failures. Sometimes they flash upon clever inventors,
but let us remember this is only after they have spent long years
studying the problem. In the case of the steam engine, however, a quite
important improvement came very curiously. Humphrey Potter was a lad
employed to turn off and on the stop cocks of a Newcomen engine, a
monotonous task, for, at every stroke one had to be turned to let steam
into the boiler and another for injecting the cold water to condense it,
and this had to be done at the right instant or the engine could not
move. How to relieve himself from the drudgery became the question. He
wished time to play with the other boys whose merriment was often heard
at no great distance, and this set him thinking. Humphrey saw that the
beam in its movements might serve to open and shut these stop cocks and
he promptly began to attach cords to the cocks and then tied them at the
proper points to the beam, so that ascending it pulled one cord and
descending the other. Thus came to us perhaps not the first automatic
device, but no doubt the first of its kind that was ever seen there. The
steam engine henceforth was self-attending, providing itself for its own
supply of steam and for its condensation with perfect regularity. It had
become in this feature automatic.

The cords of Potter gave place to vertical rods with small pegs which
pressed upward or downward as desired. These have long since been
replaced by other devices, but all are only simple modifications of a
contrivance devised by the mere lad whose duty it was to turn the