HOROLOGY. 



friction ; and, not being liable to the wear 

 which takes place in metal rubbing upon 

 metal, the machine, with that addition, 

 not only becomes more durable, but ac- 

 quires a degree of uniformity in the mo- 

 tion of the pieces, which is very favoura- 

 ble to the regularity of its going. 



That extraordinary man John Harrison 

 having produced the first portable ma- 

 chines, which, upon repeated trials, met 

 with success, to the extent required for 

 the great reward offered by the British 

 parliament, must be reckoned the father 

 of modern chronometry; and his long 

 and active career has proved extremely 

 useful, by stimulating with so bright an 

 example other artists to similar endea- 

 vours The principles of Mr. Harrison's 

 watches are well known ; and, as most 

 parts of his construction have been su- 

 perseded by more simple contrivances, 

 we shall only mention the principal inven- 

 tions of which he appears to be the au- 

 thor, and which are still used by the 

 watchmakers of the present day. 



The going fusee is one among those in- 

 ventions which have proved the most ge- 

 nerally useful in practice. By this simple 

 mechanism, the main spring, while the 

 watch is going, acts on an intermediate 

 short spring, which Harrison calls the se- 

 condary spring, and is constantly kept 

 bent to a certain tension by the former ; 

 and when the watch is winding up, and 

 the principal spring ceases to act, the se- 

 condary spring being placed in a ratchet 

 wheel, which is hindered from retrograd- 

 ing by a click, continues the motion with- 

 out alteration. Other contrivances have 

 been proposed, and executed, to make 

 time-pieces go while winding up ; but 

 none which, like this, combines the ad- 

 vantage of simplicity, and the property 

 of providing a supplementary power, 

 which is equal to that of the main spring- 

 when its action ceases. And it is to be ob- 

 served, that the utility of the going fu- 

 see, which has induced manufacturers to 

 introduce it into all good watches, is pe- 

 culiarly important in those time-pieces 

 which have not the power of setting them- 

 selves in motion, as is the case with the 

 best modern escapements. 



Harrison invented also a compensation 

 for the effects of heat and cold ; which at 

 the time was perfectly new, and has led 

 to the improvements made afterwards in 

 that essential requisite of time-keepers. 



The alterations to which the length of 

 the pendulum is liable, by the different 

 degrees of heat and cold, affect the going 

 of clocks with that sort of regulator, (see 

 PENDULUM) ; and watches, with a balance, 



are still more subject to irregularity from 

 that source ; because not only the ba- 

 lance expands or contracts, according to 

 the rise or fall of the thermometer, but 

 the regulating spring itself, while it suf- 

 fers similar changes, becomes weaker or 

 stronger; so that, from these causes, a 

 time-piece must go slower or faster in too 

 great a proportion to be overlooked or 

 neglected. Graham (Philosophical Trans- 

 actions, 1726) is the first who thought of 

 applying two metals, of different expansi- 

 bility, to correct the errors proceeding 

 from the variation of temperature in a 

 pendulum ; but as he seemed to have had 

 in view to effect it immediately, without 

 the aid of mechanism, he was obliged to 

 fix on steel and mercury, these being the 

 metals which offered to him the greatest 

 difference of dilatation and contraction. 

 Harrison, by multiplying the bars, in- 

 creased the total length of the two metals 

 acting on one another, without exceeding 

 the limits of the pendulum ; and thereby 

 produced a sufficient compensation with 

 brass and steel, in the compound or grid- 

 iron pendulum, which has been almost 

 universally adopted ever since. This con- 

 trivance could not be easily applied to 

 balances ; but Harrison, following still the 

 principle of the different expansibility of 

 metals, applied it in a manner which had 

 not been thought of before, and made it 

 act on the spiral spring, in order to pro- 

 duce the desired compensation in the re- 

 gulator. This method is described as fol- 

 lows : (Principles of Mr. Harrison's Time- 

 keeper, p. xii. notes.) " The thermome- 

 ter kirb is composed of two thin plates of 

 brass and steel riveted together in seve- 

 ral places, which, by the greater expan- 

 sion of brass than steel by heat, and con- 

 traction by cold, becomes convex on the 

 brass side in hot weather, and convex on 

 the steel side in cold weather ; whence, 

 one end being fixed, the other end obtains 

 a motion corresponding with the changes 

 of heat and cold, and the two pins at the 

 end, between which the balance spring 

 passes, and which it touches alternately as 

 the spring bends and unbends itself, will 

 shorten or lengthen the spring, as the 

 change of heat and cold would otherwise 

 require to be done by the hand, in the 

 manner used for regulating a common 

 watch." 



This kind of compensation has been 

 since applied in other ways ; but the me- 

 thod, in general, is liable to some mate- 

 rial objections, on account of its altering 

 the length of the balance spring, and the 

 difficulty, perhaps impossiblity, of ef- 

 fecting with it an accurate adjustment. 



