CHAMBERS'S INFORMATION FOR THE PEOPLE. 



period as before heating. Practically, it is found 

 that a strip of dry fir-wood, carefully varnished, 

 to prevent the absorption of moisture, is very 

 little affected by change of temperature ; and, 

 in many excellent clocks, this is used as a very 

 effective substitute for the more elaborate forms 

 just described. 



Other Improvements. 



While improvements were effecting in the 

 escapement and pendulum of clocks, the inge- 

 nuity of artists was not confined to these alone. 

 Till the beginning of the sixteenth century, clocks 

 were of great bulk, and only fit for turrets or large 

 buildings ; and although after this period they 

 were made small enough to be introduced into 

 apartments, there could be no such thing as a 

 really portable clock, far less a watch, till weights 

 and pendulums were got rid of altogether. The 

 substitution of a mainspring for a weight, therefore, 

 constituted a great era in horology, or the science 

 of time-keeping ; and this took place about the 

 middle of the sixteenth century, and was shortly 

 afterwards followed by the invention of the fusee, 

 a very necessary appendage to the mainspring. 

 But as these inventions, together with the balance- 

 spring, rather constitute peculiar features of the 

 watch than of the clock, we shall reserve the ex- 

 planation of these ingenious pieces of mechanism 

 till we come to treat of watches. Meantime, there 

 is another part of the works which requires to be 

 here noticed namely, the 



Mechanism for Striking the Hours. 



It is not known when the alarm or when the 

 striking-mechanism of the clock was first applied. 

 The alarm was adopted for the use of the Romish 

 priesthood, to arouse them to their morning 

 devotions. The first striking-clock probably an- 

 nounced the hour by a single blow, as they still 

 do, to avoid noise, in most of the Scottish 

 churches. In De Wyclc's clock, the wheel N, with 

 its projecting pins, served to discharge the striking 

 part, which it has not been thought necessary to 

 illustrate. Like other old clocks, it locked against 

 an interrupted hoop, fixed on what was called the 

 hoop-wheel; and the eleven notches on the edge 

 of the plate-wheel determined the hours, or par- 

 ticular number of blows which the hammer should 

 give. During the seventeenth century there existed 

 a great taste for striking-clocks, and hence a great 

 variety of them. Several of Tompion's clocks not 

 only struck the quarters on eight bells, but also 

 the hour after each quarter ; at twelve o'clock, 44 

 blows were struck ; and between twelve and one, 

 no less than 113 ! Many struck the hour twice, 

 like that of St Clement Danes, in the Strand, 

 London, first on a large bell, and then on a small 

 one. Others, again, were invented so as to tell 

 the hours with the least possible noise. 



The striking part of a clock is rather a peculiar 

 and intricate piece of mechanism. In ordinary 

 clocks, the impelling power is a weight similar to 

 that which moves the time-measuring mechanism 

 itself; but the pressure of this weight on the 

 striking-machinery is only permitted to come into 

 play at stated periods in course of the workings of 

 the time-keeping apparatus namely, at the com- 

 pletion of every hour ; when the minute-wheel, 

 which revolves once in an hour, and carries the 



298 



minute-hand of the clock along with it, brings it 

 into action by the temporary release of a catch or 

 detent, permitting the weight wound up on the 

 cylinder of the striking-apparatus to run down for 

 a little, in doing which, the hammer is forced into 

 action, so as to strike the bell. Whether the 

 strokes shall be one or many, is determined prin- 

 cipally by two pieces of mechanism, one called a 

 snail, from its form or outline, with twelve steps, 

 and the other a rack, with twelve teeth ; but the 

 intricate action of the whole it would be in vain 

 here to attempt to explain. Suffice it to say, that 

 the time during which the striking-weight is- 

 allowed to descend, varies according to the turn- 

 ing of the twelve steps of the snail on its axis, and 

 the position of the twelve teeth of the rack, at 

 different hours of the day ; being sometimes only 

 long enough to permit one blow to be given by 

 the hammer on the bell, and at another time long 

 enough for twelve such blows. 



The lifting piece of the rack-hook, in some 

 clocks, may be raised by pulling a string attached 

 to a small additional piece of mechanism, and 

 thus the clock is made to repeat the hour last 

 struck at any time required an addition useful 

 through the night, or to the blind. The modes, 

 however, by which clocks as well as watches have 

 been made repeaters, have been very various. 

 Repeating-clocks were first invented by Barlow, 

 an English clergyman, and executed by Tompion 

 in 1676. Some have been made to repeat both 

 hours and quarters at any time, and to indicate 

 the time by blows which might be felt but not 

 heard. 



The bells connected with clocks, especially 

 those of churches and other public buildings, are 

 often worthy of notice, either on account of their 

 gigantic size, or on account of the arrangements 

 by which they are made to perform a variety of 

 musical chimes. The largest bell in the world 

 is the 'Monarch' of Moscow, which is above 

 21 feet in diameter and in height, and weighs 

 193 tons. It was cast in 1734, but fell down 

 during a fire in 1737 was injured, and re- 

 mained sunk in the earth till 1837, when it was 

 raised, and now forms the dome of a chapel, made 

 by excavating the space below it. Another bell in 

 Moscow weighs 80 tons. The great bell of Peking, 

 13 feet in diameter, and 14 feet high, weighs 53^ 

 tons ; those of Olmiitz, Rouen, and Vienna weigh 

 nearly 18 tons. The most noted bells in Britain 

 are ' Great Peter,' placed in York Minster in 

 1845, whose weight is nearly II tons; 'Great 

 Tom ' of Lincoln, 5 \ tons ; and the great bell of 

 St Paul's, 5 tons. The bell cast for the New 

 Palace of Westminster, but afterwards cracked, 

 weighed 14 tons ; that of the Roman Catholic 

 Cathedral of Montreal, 13^ tons. The metal of 

 which bells are made is generally an alloy of 80 

 parts copper and 20 tin. 



The illumination of clocks was a favourite idea 

 in the seventeenth and eighteenth centuries, and 

 is equally useful in a public way as the striking of 

 hours or the ringing of bells. It was only during 

 the current century, however, that any plan was 

 adopted for public clocks ; the first notion being 

 to light them from without, by reflecting the light 

 of a common lamp or gas-jet on their dials. This 

 simple method is still employed, but is vastly 

 inferior to the employment of a translucent dial, 

 with a strongly reflected light from behind. 



