* Translation by Andries de Man

I) Arithmometer from 1848 (T1849)

This recently discovered splendid patent describes an astonishing tens-carry mechanism!

It is peculiar in abandoning the tens-carry wheel that was used in the other machines, from 1820 to 1880 !
Usually a freely rotating square axle is found above the drum. This axle carries 3 gear wheels (or pinions)
The first gear is connected to the cursor by a yoke and can be shifted along the square axle as a function of the multiplicand setting by the operator.
The second gear moves very easily during the tens-carry phase, in such a way that it can engage with a tooth located just below it.
The third, conical, gear transfers to the result register the number of units produced by the operation.

But this machine only contains the first shiftable gear, the one connected to the cursor!

As a consequence, to enable a tens-carry, Thomas had to lengthen the tens-carry tooth so that could engage with the movable gear A in whichever position along the position it can be: 0,1,2,3,4,5,6,7,8 or 9 .

So one sees a tooth longer than the drum itself !

To prevent the tooth from engaging all the time, Thomas constructed an extractible tooth, placed in the drum. During the tens-carry phase, the tooth leaves its slit and sticks out as far as the nine teeth of the drum. (Fig. A, B). A spring inside the drum will push a cylindrical part X located on the same axis. This part, connected to the tooth by a small perpendicular arm, will pull out the tooth . The tooth has two inclined slits that slide along two pins. If the tooth is pushed it slides along the two pins, which will raise the tooth out of the drum.

At the end of the rotation, the system is put back in its non-engaging state by a helical wedge.

Fig. A

Fig. B

II) Conclusion

It is really a funny mechanism! Although one finds a blocking pin similar to the one in T1822, as well as the helical wedge for pushing back the whole contrivance, the principle of an extractible tooth is at least original and is an excursion from the usual "Thomasian" scheme.

Thomas Arithmometer from 1848 made by Piolaine

III) Sources

"Patent N° 8282, April 25, 1849"

Extract :

« Below each dial a 10-teeth gear is mounted. The dial carries a point or small arm that triggers a detent if the dial passes from 9 to 0 or from 0 to 9 (See fig.1 & fig.2)

 Inside one sees (figure 2) stepped drums with 20 teeth, eleven of which are cut away along the whole length of the drum, while the other nine are cut away stepwise, representing the numbers 1 to 9 of the multiplicand  (see figure 5 which shows one drum, with a length of 0m07).
A tenth movable tooth is placed after the 9 teeth, as will be explained below.

 The teeth of the drum can engage with a small 10-teeth gear wheel that is guided by a yoke that is attached to the indicating knob. The small gear slides along a square axle and can be shifted according to the multiplicand digit to a position where the gear can engage the section of the steps of which the number equals the digit indicated by the setting knob.
If the drum rotates once, it turns the small gear over the number of teeth indicated by the setting knob and the dial displays the number.
The small gears are accompanied by a ratchet that is lifted by the teeth of the drum. When a gear is no longer engaged with the drum tooth, its ratchet drops and restrains the gear .

To the left of the drums is another drum, cut as a spiral (see figure 7). A slit cut along its length allows an arm led by a knob to control the number of rotations made by all the drums to represent one of the multiplicator digits.

So, if the multiplicator knob indicates N° 9, the multiplicand, which can consist of 10 digits, will be multiplied by 9.

All the drums of the multiplicand, including the multiplicator drum, engage with a sequence of gears. One of these gears is actuated by a crank handle, so that one turn of the handle causes all the drums to turn once (that set of gears is shown in figure 3).

One could get the same movement by means of a shaft running along the casing and engaging  [….] side-toothed gears, and thereby turning the drums. This mechanism is better, but more expensive. 

The drums between the first and last carry a mechanism to process tens-carries. The tenth tooth is replaced by a movable tooth, which is as long as the drum. It is hidden inside the drum (Fig. 6) and does not appear at the level of the other teeth to engage with the small gear wheels until it is required to produce a tens-carry (Fig. 6)

To enable this, the tooth is pushed out over two sloped edges by a spiral spring on the axle of the drum, see figure 6; The spring is compressed by a wedge that is mounted on the casing, pulling back the tooth for each turn of the drum; A small arm connected to the dial at the right keeps the spring compressed when there is no tens-carry to be performed, but if the dial passes from 9 to 0 or from 0 to 9, the little pin or arm of the dial detaches the ratchet, so the spring can push the tooth of the next number to the left, and the tens-carry is added when its number has been produced.

 It's now time to explain why eleven teeth of the drum are completely cut away; This void was needed to perform the tens-carries; Each drum has to receive its tens-carry after having produced its own number. This can only take place if the tens-carries are performed sequentially, the one after the other : it is therefore necessary that those for the tens are produced before the hundreds, those for the hundreds before the thousands etcetera. That's why the drums are so placed that they engage the multiplicand gears one after the other. One has to leave a 2 teeth difference between each drum; so the second drum idles for 2 teeth, the third 4 teeth, the fifth 6 teeth, the sixth 8 teeth.
Each drum should have two teeth cut away per multiplicand digit for which the machine is designed, and one tooth for the tens-carry, which makes eleven teeth for a 5-digit machine.»