370 



Hooke, in his 

 Culteiian 

 lectures, ia 

 1664, explained 

 numerous ways 

 of apply i iig 

 springs to the 

 balance, and 

 rendering its 

 vibrations 

 equal in dura- 

 tion : 



IXVEXTION OF THE BALANCE SPRIKG. 



Ilooke was long before him in the invention of the circular or 

 conical pendulum, which he introduced for philosophical pur- 

 poses, to lepresent the motion of the planets, and had proposed 

 this pendulum regulated by springs instead of gravity, for a 

 time measurer, before either Huygbens or himself thought of 

 the balance spring. It was to consist of two balls, A B, ex- 

 actly balanced round a centre, C, in the axis, C D, Fig. 3. 

 Plate XI. : when this was set a whirling- round the axis, the 

 balls would fly out at right angles at once, but they were to 

 be prevented by a spring, E F G, coiled round the centre, G>* 

 and so tapered as to produce an isochronous circulation, al- 

 though the maintaining power should vary the width of the 

 revolutions. This was exhibited at Oxford, in 1657? but did 

 not answer ; but it shows that Hooke was well acquainted with 

 the force and theory of springs. Nay, in l660, he published his 

 Micrographia ; where there is occasionally mentioned a curious 

 and paradoxial theory (as it then appeared) about the forces 

 being as the squares of the velocities, instancing a great num- 

 ber of oases, among which are expressly mentioned bows and 

 other elastic bodies, whose forces are proportional to their ten- 

 sions. In l6'7S, Dr. Ilooke published A Description of 

 Helioscopes end some other Instruments^ to which he has a 

 Postscript : in which, among other things, he says, " At the 

 " earnest importunity of a dear friend of mine since deceased, 

 " I did, in the year l664, read several of my first Cutlerian 

 '• lectures upon that subject (meaning the longitude) in the open 

 " hall ut Gresham College ; at which were present, besides a 

 " great number of the Royal Society, many strangers unknown 

 '* to mc. I there shewed the ground and reason of that applica- 

 '• tion of springs to the balance of a watch, for regulating its 

 *' motions, and explained brief!}' the true nature and principle 

 " of springs, to sliew the physical and geometrical ground of 

 " them. And I explained above twenty several ways 

 "by which springs might be applied to do the same thing, and 



" how the VIBRATIONS MIGHT RE SO REGULATED, as tO 



'" make their durations either all equal., or the greater, slower, 

 " or QUICKER than the less, and that in any proportion as- 



* Here \\c sec the spiral spring applied to this machine ; and it 

 Would be no diiiicult matter, after this, for Dr. Ilooke to apply it 

 to a vvatcli biilance. 



" signed. 



