[Sidenote: _Description of Chapin machine_]
Referring to the illustration reproducing the drawings of the Chapin
patent, the reader will note that in Fig. 1 there are four wheels
marked V. These wheels, although showing no numerals, are, according to
the specification, the numeral wheels of the machine.
The wheels are provided with a one-step ratchet device for transferring
the tens, consisting of the spring frame and pawl shown in Fig. 3,
which is operated by a pin in the lower wheel.
In Fig. 1 the units and tens wheel are shown meshed with their driving
gears. These gears are not numbered but are said to be fast to the
shafts N and M, respectively (see Fig. 2).
Fast on the shaft M, is a series of nine ratchet-toothed gears marked
O, and a like series of gears P, are fast to the shaft N. Co-acting
with each of these ratchet-toothed gears is a ratchet-toothed rack F,
pivoted at its lower end to a key-lever H, and pressed forward into
engagement with its ratchet gear by a spring G.
The key-levers H, of which there are two sets, one set with the
finger-pieces K and the other with the finger-pieces J, are all pivoted
on the block I, and held depressed at the rear by an elastic band L.
The two sets of racks F, are each provided with a number of teeth
arranged progressively from one to nine, the rack connected with the
No. 1 key having one ratchet tooth, the No. 2 having two teeth, etc.
[Sidenote: _Inoperativeness of Chapin machine_]
By this arrangement Chapin expected to add the units and tens of a
column of numerical items, and then by shifting the numeral wheels and
their transfer devices, which are mounted on a frame, designed for that
purpose, he expected to add up the hundred and thousands of the same
column of items.
It is hardly conceivable that the inventor should have overlooked the
necessity of gauging the throw of the racks F, but such is the fact, as
no provision is made in the drawings, neither was mention made of such
means in the specification. Even a single tooth on his rack F, could,
under a quick key-stroke, overthrow the numeral wheels, and the same is
true of the carry transfer mechanism.
[Illustration]
[Illustration: From the Stark Patent Drawings]
The Chapin machine, like that of Hill, was made without thought as
to what would happen when a key was depressed with a quick stroke,
as there was no provision for control of the numeral wheels against
overthrow. As stated, the machine was designed to add two columns
of digits at a time, and with an attempt to provide means to shift
the accumulator mechanism, or the numeral wheels and carry-transfer
devices, so that columns of items having four places could be added
by such a shift. Such a machine, of course, offered less than could
be found in the Hill machine, and that was nothing at all so far as a
possible operative machine is concerned.