the carrying claw of the wheel D 2 would not be detached. Meanwhile a carriage upon C 2 has been rendered necessary by the addition made in the first quarter of a turn to B 2 . This carriage takes place in the ordinary way, and would cause the dial C 2 , in the second quarter of a turn, to advance from 9 to 0: this would make the necessary preparation for a carriage from C 2 to D 2 . But unless some special arrangement was made for the purpose, that carriage would not take place during the second quarter of a turn. This peculiar contingency is provided against by an arrangement of singular mechanical beauty, and which, at the same time, answers another purpose—that of equalizing the resistance opposed to the moving power by the carrying mechanism. The fingers placed on the axes of the several dials in the row D 2 , do not act at the same instant on the carrying claws adjacent to them; but they are so placed, that their action may be distributed throughout the second quarter of a turn in regular succession. Thus the finger on the axis of the dial A 2 first encounters the claw upon B 2 , and drives it through one tooth immediately forwards; the finger on the axis of B 2 encounters the claw upon C 2 and drives it through one tooth; the action of the finger on C 2 on the claw on D 2 next succeeds, and so on. Thus, while the finger on B 2 acts on C 2 , and causes the division from 9 to 0 to pass under the index, the thumb on C 2 at the same instant acts on the trigger, and detaches the carrying claw on D 2 , which is forthwith encountered by the carrying finger on C 2 , and driven forward one tooth. The dial D 2 accordingly moves forward one division, and 5 is brought under the index. This arrangement is beautifully effected by placing the several fingers, which act upon the carrying claws, spirally on their axes, so that they come into action in regular succession.
We have stated that, at the commencement of each revolution of the moving axis, the bolts which drive the dials of the first, third, and fifth rows, are shot. The process of shooting these bolts must therefore have taken place during the last quarter of the preceding revolution; but it is during that quarter of a turn that the carriages are effected in the second and fourth rows. Since the bolts which drive the dials of the first, third, and fifth rows, have no mechanical connexion with the dials in the second and fourth rows, there is nothing in the process of shooting those bolts incompatible with that of moving the dials of the second and fourth rows: hence these two processes may both take place during the same quarter of a turn. But in order to equalize the resistance to the moving power, the same expedient is here adopted as that already described in the process of carrying. The arms which shoot the bolts of each row of dials are arranged spirally, so as to act successively throughout the quarter of a turn. There is, however, a contingency which, under certain circumstances, would here produce a difficulty which must be provided against. It is possible, and in fact