From the preceding description it is evident, that when any of the elliptic plate pins come to press clown that end of the long arm which lies near and under them, the forked end will raise up the grooved socket, and the segment which is connected with it ; hence the teeth of the segment will meet with pins which are at the back of the month ring, and by their means will turn the month ring. On the month wheel is fixed a pin, which, in common, shifts the day of the month ring ; but in those months in which there are only 30 days, the pins in the elliptic plate, which press down the end of the arm, make the segment be pumped up only so far as to meet with one of the pins at the back of the month ring, which is a little longer than the other two; and one day being shifted by it, and another by the fixed pin in the month wheel, this makes the shifting from the 30th to the 1st clay of the succeeding month. The pin in the elliptic plate for the month of February being longer than the others presses the end of the arm a little more clown, consequently the pumping up of the segment must be to a greater height ; by this means the three teeth on the segment get hold of the three pins on the back of the month ring; this, with the fixed pin in the month wheel, are ready to shift four teeth of the month rilg, viz. from the 28th of February to the 1st of 'March ; and, by this very ingenious sort of mechanism, the month ring shows always the right day of the mouth, except on the 29th of February in leap-years. It may be necessary to notice, that the fixed pin in the day of the month wheel must be placed at such a distance frond the first tooth on the segment, as is equal to the space between the teeth on the segment. The month ring is not attached by rollers to the back of the dial in the usual way, but runs in four rollers, which are fixed on four brass studs on the fore frame plate. This is for the con veniency of seeing more easily the operations of the seg ment with the month ring, when the segment is pumped up and down.
The construction of the month wheel, and of the ap paratus for shifting the month ring, will be better under stood from Figs. 8 and 9, where AA is the month wheel ; B, B, two arms or crosses nearly similar to those of the month wheel, having a hole in the centre which goes free ly on the upper socket of the month wheel ; on one of these arms is a segment of a circle, nearly of the same ra dius as that of the month wheel, having three teeth cut on it, like those of the month ring ; a, a, are two brass pillars rivetted on the upper side of the month wheel, the upper ends being formed into a sort of pivots ; on these and the month wheel socket, the segment is made to move freely up and down. C is a rectangular piece of brass, into which a socket is rivetted, which moves up and down on the lower socket of the month wheel, having a groove turned out on it, which receives the forked end of the arm, which pumps it up and down ; b, b, are two small brass pillars, which are rivetted also into the rectangular piece of brass, having two holes in the month wheel, through which they pass easily up and down ; the other ends of them go into the segment at b, b, and are screwed to it by means of two small screws. On one of the arms
of the month wheel is screwed a small kneed sort of cock d, having a pin fixed in it, for turning the day of the month ring in the usual manner.
On Repeating Clocks and Watches.
To those who do not sleep well, nothing can be more convenient and useful than a repeater, whether it is in a watch, or in a small fixed clock. A history of this inven tion is given by Mr Denham in his Artificial Clockmake;. Berthoud, in his Histoire, has given the following account of it, which is taken chiefly from Denham.
" The art of measuring time, (says Berthoud,) was again enriched with two fine and useful inventions before the end of the seventeenth century. One was the equation clock ; the other, which is the most precious, and of the most ge neral utility, is that kind of striking which has been called repeating. It is of the most ingenious mechanism, and when added to a clock, serves to make known at pleasure, at every instant of the clay or night, without seeing the dial, the hour and the parts of the hour, which are pointed out by the hands of the clock. Both these inventions are due to the English artists." " The clocks in question hire, (says Denham.) are those which, by means of a cord, when pulled, strike the hours, the (platters, and even some the minutes, at all times of the day and of the night. This striking or repeating was invented by a Air Barlow, towards the end of the reign of King Charles II. in 1676." It is not mentioned by Denham. whether Barlow was a watchmaker or not. lATe have heard it said by old wat,:h makers, that he was a clergyman. This seems in some measure confirmed, by his having applied to Tompion to make his repeating watch, when he was about to obtain a patent for the invention.
" This ingenious invention," continues Berthoud," which had not been before thought of, made at the outset a great noise, and much engaged the attention of the London watchmakers. On the idea alone which each formed of it, they all set to work to try the same thing, but by very dif ferent ways ; whence has arisen that great variety in the work of repeating motions, which was seen at this time in London.
" This discovery continued to be practised in chamber -clocks until the reign of James II. It was then applied to pocket watches. But there arose disputes concerning the author of the invention, of which I shall simply relate the facts to the reader, leaving him to judge of it as he thinks proper." Towards the end of the reign of James II. Mr Barlow applied his invention to pocket watches, and employed the celebrated Tompion to make a watch of this kind accord ing to his ideas; and at that time, conjointly with the Lord Allebone, chief justice, and some others, he endeavoured to obtain a patent for it.