3^GG INVENTION OF THE BALANCE SPRIKG, 



enough to discover the cycloid, though he makes a most beauti- 

 ful guess at it, and one of the best accounts of its properties that 

 has been given. He says that the vibrations will be equal it' 

 3'^ou could make the pendulum move in such a curve as this : 

 The small arches ab,bc,cd, de, &c. Fig. 2, Plate XL, being ali 

 equal, the perpendicular heights of them BO, Cc, Dd, Ee, &c., 

 —which was must increase as the numbers 1, 2,3, 4, &c. Now this is pre- 

 hivestb-ated by ^'-^'j ^'""^ property of the cycloid discovered about eight years 

 Huyghens. afterwards by M. Huyghens. Huyghens at the same time 

 was speculating on this subject ; and his father, who had 

 been at Oxford, kept up a correspondence with the learned 

 there. Huyghens being a consummate mathematician, soon 

 investigated the motion of the pendulum, and by this time had 

 conceived theprojectof getting a reward and a monopoly.- His 

 father was a member of the Slates General, and it was about 

 this very 3'ear that they offered a reward of 10,000 florins. It 

 is not improbable but he knew of his son's researches, and was 

 The first clock a means of procuring this act of the States. About the year 

 wIthTSu- ^^'^''^' ^^ (Huyghens) presented his first clock (not with a cy- 

 Sum. cloid) to the States. It is not in the least probable, that a per- 



son, aiming at a monopoly and a public re\vard, would divulge 

 his secrets, or that Mr. Hooke, at Oxford, would be informed 

 of what he was doing. It is much more likely that the experi- 

 ments and projects of the curious gentlemen at Oxford (who 

 never made any secret of their operations, indeed durst not, 

 because their meetings were suspected, and frequently visited 

 by Cromwell's soldiers) might be known to Huyghens. We 

 know for certain that Mr. Oldenburgh actually did communi- 

 cate every thing to his countrymen. Be this at it may, Huy- 

 ghens at this time thought of nothing but his cycloidal pendu- 

 Hooke, in 1658, lum, nor for several years after. But in l65S, Hooke searched 



discovered the .^\)Q^f for a force proportional to the distance from the place 



isochroiiism ' ' . 



of sprinji,s. of rest, and found, experimentally, that springs had this pro- 

 perty/. He kept this a secret, but gave it to his friends in the 

 following cypher : " ee, i it, n 0, ss s, tt, uu ;" which was after- 

 wards (in 1661) explained, " Ut tensio .sic vis," i. e. As the 

 tension, so is the force. He told Mr. Boyle that this was a 

 secret for constructing pocket watches for the longitude, and 

 showed him a watch, which was declared by Mr. Boyle to keep 

 within half a minute a day ; a thing infinitely beyond any watch 

 then known. 



Iramedi- 



