Book IX. Mechanic Powers. 187

ance of bending, but alſo the other of rubbing, or weaving ofone volute upon the other, which reſiſtance nevertheleſs it hathby accident. ö

Fourtbly, Springs are made weaker by degrees by often draw-ing them, but they are more weakned if they never reſtorethemſelves, but if always, or for a long time, they continuedrawn or pull'd; hence they have greater force in the firſt ma-king of an Engin, but leſſer after long uſing tbem.

Fifiblh, if they remain ſometime free, that is, without draw-ing, they recover ſome of their ſtrength which they had loſtbefore.

Sixthly, Fo. Helmont in his Book entituled Med. Phyſic. de tem-pore, Num. 5 O. affirms, That the ſaid Springs of Clocks or Wat-ches are wont to be more ſtrong, or ſtubborn, When the NorthWind blows, which notwithſtanding is not as yet well knownto me, neither doth the cauſe of this Phænomenaà euſily appcar,unleſs you'll ſay from Cold, which is wont to be more rigidwhen the Wind is Northward.

Theſe things being noted, the irregular force of Springs maybe reduced to uniformity divers ways: Firſt, when theſe thinpieces of Mettal are wont to be made every where of the ſamebreadth and thickneſs, they exert their force unequally in thebeginning and in the end; if the parts near the Centre bemade thicker than the other, or broader with a due propor-tion, and then the drawing to, or lapping up being made inthe Centre, the reſiſtance will be equal and uniform in thewhole drawing, or wreathing, and conſequently they willmake the force equal in their whole reſtitution, until theycome to their firſt ſtate, or condition; moreover on the con-trary, if they are made thicker in the parts neareſt the circum-ference, and then the drawing be made in the circumference,from the oppoſite reaſon there will be an inequality of forceto compenſate or amend that unequal thickneſs or brendth ofthe thin plate; notwithſtanding this way, whereby the inequa-lity of this thickneſs compenſates, the inequality of force is notuſed, perhaps becauſe tis more laborious, and neither is it ca-ſy to find the proportion, whereby the thickneſs ouglit to beincreaſed gradually; yet if it were reduced into practicc, iiwould be far more uſeful and certain than the other.

The ſecond way more obvious, and uſed in regulating theSprings in ancient Watches, ig by an uncqual preſliom f

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