CHAMBERS'S INFORMATION FOR THE PEOPLE. 



and intricate forms. It will, moreover, shew the 

 general mode of construction adopted in the four- 

 teenth century, including the balance with weights, 

 by which the motion was then regulated, instead 

 of as now by a pendulum. 



General Movement and Regulation of Clock-work. 



Without requiring to enter into any very minute 

 detail of the manner in which motion in a clock 

 or watch is successively communicated from one 

 toothed-wheel G or I, 

 or pinion e or g, to 

 another, it will be 

 readily understood 

 that the weight A 

 below the clock-work, 

 wound up by a cord 

 on the cylinder B, in 

 its constant tendency 

 to fall to the ground, 

 will cause the cylin- 

 der to turn round on 

 its axis ; and thus one 

 toothed wheel or pinion 

 will set another in 

 motion, till the move- 

 ment be communi- 

 cated to the crown- 

 wheel, escapement- 

 wheel, or wheel of 

 rencounter (I), the 

 teeth of which so act 

 on the two small levers 

 or pallets (/, K) pro- 

 De Wyck's Clock. jecting from, and 



forming part of, the 



suspended upright spindle or vertical axis (KM), 

 on which is fixed the regulator or balance (LL), 

 that an alternating or vibratory instead of a 

 circular motion of the balance itself will be 

 the result. The rotatory motion of the wheel- 

 work, in short, will be converted into a vibratory 

 motion by the alternate catching of the levers by 

 the teeth of the crown or escapement wheel, and 

 their alternate escape from them. 



Were it not for some such check, it is manifest 

 that the weight would go on descending with a 

 rapidly increasing speed till it reached the ground. 

 It is this rapid accelerated motion which begins 

 in a modern clock whenever the pendulum is 

 taken away. To prevent this rapid unwinding of 

 the clock-work, then, and to adjust it to the more 

 deliberate measurement of time, we have, in De 

 Wyck's clock, the balance loaded with two weights 

 (m, m) ; and the further these are removed from 

 the axis or spindle (KM), the more heavily will 

 they resist and counteract the escapement of the 

 levers and the rapidity of the rotation of the 

 escapement-wheel, till the clock be brought to go 

 neither too quick nor too slow. The want of a 

 regulation spring, however, must have rendered 

 these machines very imperfect. 



Pendulum and Escapement. 



What the balance and the weights attached to 

 it were to clocks of an ancient date, the pendulum 

 is, in general, to modern clocks. The measure- 

 ment of time being thus regulated by the oscil- 

 lations of the pendulum, this part of the mechan- 



296 



ism of a clock, including the escapement, is of 

 primary interest and importance. 



Galileo, the great astronomer, when a student at 

 Pisa, happened to discover, while engaged in the 

 cathedral there not in meditating on the impos- 

 ing ceremonial of the Catholic Church, which was 

 then in progress, but in what, to many a good 

 Catholic, would undoubtedly have seemed the 

 vacant, idle, and profane contemplation of the 

 lamps which swung from the roof that the oscilla- 

 tions of a pendulum, whether great or small, are 

 performed in equal times in the same pendulum 

 an important fact, the truth of which he tested, 

 not by the beats of his watch (for no such instru- 

 ment then existed), but by the beats of a natural 

 time-keeper to which we have not yet alluded 

 namely, the pulse. The law that the time of 

 vibration of a pendulum increases, not as the 

 length, but as the square root of the length- in 

 other words, that a pendulum to beat seconds 

 must be four times the length of one that beats 

 half-seconds as also the variation of the length 

 with the latitude of the place, are fully described 

 in the number on MATTER AND MOTION. The 

 greatest possible nicety, indeed, is required in the 

 adjustment of the length ; for a difference, if in 

 extent amounting to the icooth part of an inch, 

 would cause an error of about one second a day ; 

 therefore, to make a pendulum go slower by one 

 second a day, it must be lengthened by the loooth 

 part of an inch ; and to make it go quicker, it 

 must be shortened in the same proportion. 



It does not appear that Galileo ever applied the 

 pendulum to the regulation of time-keepers. Who 

 was the first to do so, is disputed ; but as Hiiygens, 

 an ingenious Dutchman, about 1657, made a more 

 scientific and efficient application of it than had 

 been done before, he is generally held to be the 

 inventor of the pendulum-clock. Hiiygens, in 

 adapting the pendulum to the mechanism pre- 

 viously invented, had little more to do than simply 

 to add a new wheel to the movement, so as to 

 enable him to place the crown-wheel and spindle 

 in a horizontal instead of a perpendicular position, 

 that the lower arm of the balance then, of course, 

 perpendicular, instead of horizontal, as in De 

 Wyck's clock might be extended, as it were, 

 downwards, and thus, in fact, be converted into a 

 pendulum. The principle of construction adopted 

 by Hiiygens, from the peculiar action of the levers 

 and spindle, required a light pendulum and great 

 arcs of oscillation ; and although, to secure isoch- 

 ronous vibration in these large arcs, the ingenious 

 device of constraining the motion in a cycloidal 

 curve was resorted to, yet the consequence was, as 

 has been remarked, that ' Hiiygens's clock governed 

 the pendulum, whereas the pendulum ought to 

 govern the clock.' About ten years afterwards, 

 the celebrated Dr Hooke invented an escapement, 

 which enabled a less maintaining power to carry 

 a heavier pendulum. The pendulum, too, making 

 smaller arcs of vibration, was less resisted by 

 the air, and therefore performed its motion with 

 greater regularity. This device is called the 

 crutch or anchor escapement. It was brought by 

 Hooke before the notice of the Royal Society in 

 1666 ; and was practically introduced into the art 

 of clockmaking by Clement, a London clock- 

 maker, in 1680. It is the form still most usually 

 employed in ordinary clocks. It regulates the 

 motion as follows : The pendulum is fixed at A, 



