96 CHRONOMETERS. 



number of minutes after the hours which the index 

 last left in its motion. The small hand B, in the 

 nich at top, goes round once in a minute, and 

 shows the seconds. The wheel-work of this clock 

 may be seen in Fig. 4. A is the first, or great 

 wheel, containing 160 teeth, and going round in 

 four hours with the index A, in Fig. 3. let down 

 by a hole on its axis. The wheel turns a pinion 

 of ten leaves, which therefore goes round in a 

 quarter of an hour. On the axis of this pinion is 

 the wheel C, of 120 teeth, which goes round in 

 the same time, and turns a pinion, D, of eight 

 leaves, round in a minute, with the second-hand, 

 B, of Fig. 3. fixed on its axis, and also the common 

 wheel E, of 80 teeth, for moving a pendulum (by 

 palettes,) that vibrates seconds as in a common 

 clock. This clock is wound up by a cord going 

 over a pulley on the axis of the great wheel, like a 

 common thirty-hour clock. Many of these very 

 simple machines were constructed, which mea- 

 sured time exceedingly well. It is subject, how- 

 ever, to the inconvenience of requiring frequent 

 winding, by drawing up the weights, and likewise 

 to some uncertainty as to the particular hour shown 

 by the index A. Mr. Ferguson has proposed to 

 remedy these inconveniences by the following con- 

 struction : in the dial-plate of his clock (Fig. 5.) 

 there is an opening, abed, below the centre, 

 through which appears part of a flat plate : on this 

 the twelve hours, with their divisions into quarters, 

 are engraved. This plate turns round in twelve 

 hours, and the index A points out the true hour, 

 &c. B is the minute-hand, which goes round the 

 large circle of 60 minutes, whilst the plate, a b c d y 

 shifts its place one hour under the fixed index, A. 

 There is another opening, e f g h y through which 



