Part 7

This combination was timed so that the (1) key would add one, the (2) key would add two, etc., up to nine for the (9) key. Thus the prime actuation of each wheel was made safe and positive.

Before explaining the means by which the carry of the tens was effected in the Felt machine without interfering with multiple-order prime actuation, it will perhaps help the reader to recapitulate on what the Art already offered.

Going back to the Art, prior to Felt’s invention, there are a few facts worth reconsidering that point to the broadly new contributions presented in the Felt invention, and combining these facts with a little theory may perhaps give a clearer understanding of what was put into practice.

In most lines of mechanical engineering in the past, the term “theory” connected with mechanical construction was a bugaboo. But the solution of the modern calculating machine was wholly dependent upon it.

Let us summarize on the Art, prior to Felt’s invention. A calculating machine that would calculate, if we eliminate the key-driven feature, was old. The key-driven feature applied to adding mechanism was old as adapted to a single-order machine with a capacity for adding only a single column of digits.

Hill attempted to make a multiple order key-driven machine, but failed because he did not theorize on the necessities involved in the physical laws of mechanics.

Hill saw only the columnar arrangement of the ordinal division of the keyboard, and his thought did not pass beyond such relation of the keys for conveyance. There is no desire to belittle this feature, but it did not solve the problem that was set forth in the specification and claims of his patent; neither did it solve it for anyone else who wished to undertake the making of such a machine.

The introduction of keys as a driving feature in the calculating machine Art demanded design and construction suitable to control the new idiosyncrasies of force and motion injected into the Art by their use, of which the elements of inertia and momentum were the most troublesome.

Hill, in the design and construction of his machine, ignored these two elementary features of mechanics and paid the penalty by defeat. The tremendous speed transmitted to the parts of a key-driven machine, which has already been illustrated, required that lightness in construction which is absolutely necessary to reduce inertia to a minimum, should be observed. The Hill machine design is absolutely lacking in such thought. The diameter of the numeral wheel and its heavy construction alone show this. Lightness of construction also enters into the control of momentum when the mechanism must suddenly be brought to a dead stop in its lightning-speed action. A heavily-constructed numeral wheel like that shown in the Hill patent would be as hard to check as it would to start, even if Hill had provided means for checking it.

Strength of design and construction, without the usual increase in weight to attain such end, but above all, the absolute control of momentum, were features that had to be worked out.

Robjohn partly recognized these features, but he limited the application of such reasoning to the prime actuation of a single order, and made nothing operable in a multiple key-driven machine.

Spalding and Bouchet recognized that the application of control was necessary for both prime actuation and carrying, but, like Robjohn, they devised nothing that would operate with a series of keys beyond a single order.

An operative principle for control under prime actuation was perhaps present in some of the single-order key-driven machines, but whatever existed was applied to machines with keys arranged in the bank form of construction, and, to be used with the keys in columnar formation, required at least a new constructive type of invention. But none of the means of control for carrying, prior to Felt’s invention, held any feature that would solve the problem in a multiple-order machine.

While all the machines referred to have not been illustrated and described here, fair samples of the type that have any pertinence to the Art have been discussed, and those not illustrated would add nothing more than has been shown. A classification of the inventions referred to may be made as follows:

Parmelee and Stetner had no carrying mechanism; Hill, Robjohn, Borland and Hoffman, Swem, Lindholm and Smith had no control for the carry. Carroll, Bouchet and Spalding show a control for the carrying action, which in itself would defeat the use of a higher wheel for prime actuation, and which obviously would also defeat its use in a multiple-order key-driven machine.

One of the principal reasons why theory was necessary to solve the problem of the key-driven calculator existed in the impossibility of seeing what took place in the action of the mechanism under the lightning speed which it receives in operation. Almost any old device could be made to operate if moved slow enough to see and study its action; but the same mechanism that would operate under slow action would not operate correctly under the lightning-speed action they could receive from key depression. Only theoretical reasoning could be used to analyze the cause when key-driven mechanism failed to operate correctly.

Referring again to the drawings of the Felt patent, which illustrate the first embodiment of a multiple-order key-driven calculating machine, we find, what Felt calls in the claims and specifications, a carrying mechanism for a multiple-order key-driven calculating machine. This mechanism was, as set forth in the specification, a mechanism for transferring the tens, which have been accumulated by one order, to a higher order, by adding one to the wheel of higher order for each accumulation of ten by the lower order wheel. This, in the Felt machine, as in most machines, was effected by the rotation of a numbered drum, called the numeral wheel, marked with the nine digits and cipher.

The term “transfer device” for such mechanism was in common use, and as a term it fits certain parts of all classes of devices used for that purpose, whether for a crank-driven, key-driven, or any other type of multiple-order or single-order machine. But in the Felt invention we find it was not the simple device generally used for transferring the tens. It was, in fact, a combination of devices co-acting with each other which, in the specification of the patent, was termed the carrying mechanism.

Now, carrying mechanism may in a sense be termed a transfer device, as one of its functions is that of transferring power to carry the tens, but a mere transfer device may not be truthfully termed a carrying mechanism for a multiple-order key-driven machine unless it performs the functions that go to make up a correct carrying of the tens in that class of machine, and which we find laid down under the head of carrying mechanism in the Felt patents, where we find the first operative carrying mechanism ever invented for a multiple-order key-driven machine.

The functions demanded of such a piece of mechanism are as follows: First, the storing of power to perform the carry; second, the unlocking of the numeral wheel to be carried; third, the delivery of the power stored to perform such carry; fourth, the stopping and locking of the carried wheel when it has been moved to register such carry; and fifth, clearing the carrying-lock during prime actuation. A seemingly simple operation, but let those who have tried to construct such mechanism judge; they at least have some idea of it and they will no doubt bow their heads in acknowledgment of the difficulties involved in this accomplishment.

Mechanism for carrying the tens in single digit adders was one thing, and such as was used could well be called a transfer device; but mechanism for carrying the tens in a real key-driven calculating machine was another thing, and a feature not solved until Felt solved it, and justly called such combination of devices a “carrying mechanism.”

In the Felt machine, the carrying mechanism consisted of a lever and ratchet pawl action, constructed of the parts M, m², operated by a spring m, the pawl acting upon the numeral wheel pins T, to ratchet the wheel forward under the spring power. The power in the spring was developed from the rotation of the lower wheel, which through the means of an envolute cam attached to left side of each wheel, operated the carrying lever in the opposite direction to that in which it was operated by the spring. As the carrying lever passed the highest point of the cam spiral and dropped off, the stored power in the spring retracted the lever M, and the pawl m², acting on the higher order wheel pins T, and moved it one-tenth of a revolution.

NOTE: As all the drawings of the Felt patent are not reproduced here, the cam is not shown.

This part of the mechanism was in principle an old and commonly-used device for a one-step ratchet motion used in the carry of the tens. It served as a means of storing and transferring power from the lower wheel to actuate the higher wheel in a carrying operation, but a wholly unqualified action without control.

In the Felt machine a spring-actuated lever N, mounted on the same axis with the carrying lever, and provided with a detent stop-hook at its upper end, served to engage the numeral wheel at the end of its carried action, and normally hold it locked.

An arm or pin P, fixed in and extending from the left side of the carrying lever and through a hole in the detent lever, acted to withdraw the detent lever from its locking engagement with the numeral wheel as the carrying lever reached the extreme point of retraction; thus the wheel to be carried was unlocked.

Pivoted to the side of the detent lever is a catch O. This catch or latch is so arranged as to hook on to a cross-rod q, especially constructed to co-act with the catch and hold the detent lever against immediate relocking of the numeral wheel as the carrying lever and pawl act in a carrying motion. The latch has a tail or arm p, which co-acts with the pin P on the carrying lever in such a way as to release the latch as the carrying lever finishes its carrying function.

Thus the detent lever N is again free to engage one of the control or stop-pins T to stop and lock the carried numeral wheel when the carrying lever and pawl, through the action of the spring stored in the carrying, has moved the wheel the proper distance.