Fatton's, for an Astronomical Instrument or Watch. 297

which mechanism being instantaneously put in action by the pressure of the finger, produces marks upon the plate corresponding to the minute divisions of time, which marks may be referred to after the observations are completed, and, by that means, a transit, occultation, or other celestial appearance, may be observed and recorded with a greater degree of exactness than by any other time-piece heretofore made.

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Plate XVI. Fig. 1, represents the external appearance of the instrument, and Fig. 2 the same as it would be seen if the dial plate were removed: Fig. 3 shews (upon an enlarged scale) a vertical section of the same, supposing the ordinary spring barrel, fusee, escapement, and other known parts of the watch, removed, the letters referring to the same parts, respectively, in each figure. The situation of the escapement wheel is shewn by dots, at e, having, upon its arbour, a pinion, which engages into the teeth of the wheel, b, the axle of which carries a revolving dial plate, c, fig. 1: this wheel revolves in one minute, and indicates seconds of time. Upon the axle of the wheel, b, is a pinion of eight teeth, taking into a wheel, d, of seventy-two teeth, immediately under the wheel, e, seen at Fig. 3. At the upper part of the axle of d, is the wheel, e, of sixty teeth, taking into the small wheel, f, of thirty teeth, which has, upon its arbour, a pinion of two leaves engaging in the teeth of the wheel, g; of one hundred and twenty teeth. The axle of this last wheel carries the hour hand, as seen at Fig. 1, and makes one revolution in five hours. The teeth of the small wheel, f, also takes into the wheel, h, of sixty teeth, which carries the minute hand, and makes one revolution in ten minutes.

Upon the arbour of the wheel, h, there is a snail acting

against the beak or projecting part of the sliding plate, i; which plate moves upon a pivot, at j, and is pressed against the periphery of the snail by the force of a spring, *. On the sliding plate, i, there is affixed a small forked standard, which, by means of screw pivots, carries the lever, 7: under the shorter arm of this lever, which is a detent, there is a spring, x, raising it, and causing the longer arm to be depressed. At the axis, also, of the lever, there is a small detent, %, projecting downwards, nearly at right angles, to the lever. The lower end of this detent is acted upon by the points of the star wheel, m, which turns upon a pivot fixed into the plate, i, and is kept with its points always in one direction, by means of a small spring carrying a double inclined plane or wedge piece, n, that falls in between the points of the star wheel. This star wheel is moved round, one tooth at a time, by the bent lever, o, which turns upon a pivot, at p. The short arm of this bent lever is in contact with the end of a stud, q, placed on the outside of the case for the finger to act upon it.

When the stud, q, is pressed by the finger of the person who holds the watch, the end of the stud is forced against the short arm of the bent lever, o, and, by that means, causes the reverse end of the lever, o, to advance, which, bearing against one of the points of the star wheel, moves it forward one point, or tooth. An opposite point of the star wheel in contact with the detent, %, by this action of the lever, o, causes the detent, %, to advance and raise the longer arm of the lever, 7, until the point, or tooth, of the star wheel has escaped from the detent, %; when the spring, x, instantly exerts itself, and forces the long arm of the lever suddenly down, by the impetus of which, its nib strikes against the revolving dial. The wedge piece, n, now falls in

Fatton's, for an Astronomical Instrument or Watch. 299

between the points of the star, and places it in a proper position, ready to repeat the action. The action of the mechanism thus described is so sudden, that a person may cause the nib to strike the revolving dial five or six distinct blows in each second of time, if required for a rapid succession of observations.

In order to prepare the instrument for action, the main spring must be wound up, but its motion may be suspended by means of a stop, as in ordinary stop watches. After this the arm, or lever, l, should be raised up, and a minute quantity of colouring matter introduced by a camel-hair pencil into the nib, r, which is connected by a spring to the lever, . This colouring matter may be prepared by grinding tripoli, or any other colouring matter, with olive oil. When this is done, the lever is left at liberty, and the spring prevents the nib from touching the revolving dial-plate, e, until acted upon by the stud and levers, as above described.

The minute hand of the small dial-plate should be placed at 10, and the revolving dial-plate, c, turned round, until the number 60 be brought opposite the end of the lever. See fig. 1. In this situation the nib containing the colouring matter will be near the outer circumference of the revolving dial-plate. Now, suppose it be required to register, by this instrument, the precise instant of time, to the fractional part of a second, at which one body or object passes another. First, observe the time of day by any good watch, and then, by liberating the stop, put this improved watch in action at a known determinate time, holding the instrument in the hand, with the end of the forefinger bearing slightly against the stud, q. While the instrument is in action, the divisions upon the face of the revolving dial-plate, pass regularly under the nib, 7, of the lever, , but without

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being touched by the nib, and the minute hand advances one division during an entire reyolution of the dial-plate, c. When the instant arrives at which it is necessary to note an observation, the stud, q, is pressed by a sudden mo* tion of the fore-finger, which causes the lever, l, to rise and fall instantaneously by the operation of the star wheel, as above described. This action, having caused the nib to strike slightly upon the surface of the revolving dialplate, a small dot of the colouring matter is then deposited, but as the nib instantly rises, and the plate keeps revolving, any number of dots may be thus made to note a succession of observations, without the necessity of referring to the watch until after the whole of the observations are completed.

This instrument is capable of marking distinctly, upon the revolving dial-plate, a series of observations during ten minutes, without interruption or danger of one mark or dot interfering with another; for, as the dial plate revolves, the dots are arranged in a spiral direction. This is effected by the lever, b, (which carries the marking nib,) and advancing as the movement of the watch goes on, by means of the snail upon the axle of the minute wheel, h, acting against the sliding piece, i. So that the dots arrange themselves in a spiral curve, commencing from the circumference, and approaching towards the centre of the plate in the course of the ten revolutions of the minute hand, in each of which revolution the minute is known by discerning the number of curves from the circumference, upon the revolving plate, c, and the second is known by the radiant lines, between or upon which the dots of colour fall: at the end of ten minutes, the beak, at the end of the sliding plate, drops from the larger to the smaller part of the snail, ready for another operation, the winding-up of the instrument continuing its motion five hours.