The number of arms or crosses to be put in a wheel is usually decided by the taste of the person making the clock. There is, however, another view of the subject, which I would like to mention. With the same weight of metal a wheel will be stronger with six arms than with four or five, and as lightness, combined with strength, should be the object aimed at in making wheels, I prefer six arms to four or five for the wheels of a regulator.

Figs. [157] and [158] are front and side elevations of the proposed regulator movement, showing the size and position of the wheels, the size of the frames, the positions of the pillars, dial feet, etc. The dotted large circular lines on [Fig. 157] show the position the hour, minutes, and seconds circles will occupy on the dial. According to the ordinary rules of drawing, the dotted lines would infer that the movement is in front of the dial, and perhaps it may be necessary to explain that in the present instance these lines are made dotted solely with the view of making the diagram more distinct, and are not intended to represent the dial to be at the back of the movement. A is the barrel, B is the great wheel, which turns once in twelve hours; C is the hour wheel, which works into the great wheel, and also turns once in twelve hours; D is the center wheel, which turns once in an hour, and carries the minute hand; E is the third wheel, and F is the scape wheel, which turns once in a minute and carries the seconds hand; G is the pallets; H the pillars, and I is the dial feet; J is the maintaining power click, and K shows the position of the cord. Neither the hour or great wheels project over the edge of the frame, and it will be observed that a clock of this arrangement is remarkable for its simplicity, having only four wheels and three pinions, with the addition of the scape wheel and the barrel ratchets. There are no motion or dial wheels, the wheel C turning once in 12 hours, carrying the hour hand. The size and shape of the frames and the position of the pillars, allows the dial feet to be placed so that the screws which hold the dial will appear in symmetrical positions on the dial.

Formerly the term “astronomical” was applied to clocks which indicated the motions and times of the earth, moon, and other celestial bodies, but at present we may take it as indicating such as are used in astronomical observatories. In all essential particulars they are the same as first-class watchmakers’ regulators, the most obvious departure being that the hour hand is made to revolve only once a day, the dial being divided into twenty-four hours. This only requires an intermediate wheel and pinion in the motion work, and, assuming the hour hand to be driven from the center arbor, there will be the usual hour and minute wheels and cannon pinion. The most suitable ratio for these are ¼ and ⅙ = ¹⁄₂₄, and, as any numbers, being multiples, may be used, they may as well be selected so as to be cut with the same tools as the wheels of the train. Two pinions of 20 and wheels of 80 and 120 suit very well; 20 ÷ 80 and 20 ÷ 120 = ²⁰⁄₈₀ × ²⁰⁄₁₂₀ = ⁴⁰⁰⁄₉₆₀₀ = ¹⁄₂₄, and the hands will both go in the same direction.

Some astronomical clocks show mean solar, and others sidereal time; this requires no structural alteration, merely a little shortening of the pendulum in the latter case, which can be done with the regulating nut.

LIST OF ILLUSTRATIONS.