Lectures de Potentia Restitutiva, or of Spring

From this principle, it will be easy to calculate the various strengths of bows, such as longbows or crossbows, whether they are made of wood, steel, horns, sinews, or similar materials. This also applies to the ballista original: Balista; a large ancient missile launcher or catapult original: Catapulta used by the ancients. Once these strengths are determined and tables of their values are calculated, I shall shortly show a way to calculate the power they have in shooting or casting arrows, bullets, stones, grenades, or the like.

From these principles, it will also be easy to calculate the proportionate strength of a watch spring acting upon its fusee original: Fusey; a cone-shaped pulley used in old watches to equalize the pull of the mainspring, and consequently, how to adjust the fusee to the spring so as to make it drive or move the watch always with an equal force.

From the same principle, it will be easy to explain the reason for the isochronous original: Isochrone; occurring in equal periods of time motion of a spring or a stretched string, and the uniform sound produced by those whose vibrations are quick enough to produce an audible sound. Likewise, it explains the reason for sounds and their variations in all types of resonant or spring-like bodies; I will discuss more on this on another occasion.

From this, the reason appears—as I shall show shortly—why a spring applied to the balance of a watch makes its vibrations equal, whether they are larger or smaller. I showed a watch of this kind to the Right Honourable the Lord Viscount Brounker, the Honourable Robert Boyle, Esq., and Sir Robert Moray in the year 1660, in order to have obtained letters patent A government grant of exclusive rights or a monopoly for an invention for its use and benefit.

From this, it will be easy to make a "philosophical scale" A scientific weighing device to examine the weight of any body without needing to add counter-weights. This was the device I mentioned at the end of my description of Helioscopes Instruments for observing the sun without injury to the eyes, the fundamental principle of which was hidden under this anagram: c e d i i n n o o p s s s t t u u. This stands for Ut pondus sic tensio Latin: "As the weight, so the tension." This is the classic statement of Hooke's Law.. See the construction of this scale in the first three figures.

I designed this scale in order to examine the gravitation of bodies toward the center of the earth,