France · 1861 (published memoir)
Theory of Balance-Spring Terminal Curves
Partially verifiedGave adjusters a calculable basis for overcoil design and improved isochronism.
Phillips published a mathematical treatment of the terminal curves needed for concentric development of the balance spring, formalising what Breguet had achieved empirically.
Background
Édouard Phillips was a French engineer and mathematician who investigated the stability of chronometer balance spring oscillations. In 1861, Phillips published a theoretical study addressing the issue of isochronism in balance springs. He sought to address the requirement for a balance spring that maintains a constant period of oscillation regardless of amplitude, a property known as isochronism. Through his research, Phillips mathematically determined that a balance spring is isochronous if its center of gravity coincides with the balance wheel's axis.
Written from the encyclopedia entries listed under Sources; each statement was checked against the cited text.
Later history
- Phillips published a second related memoir on the regulation of watch and chronometer springs in 1864.
- Later horological research concerning the effects of friction and temperature variations on these springs was continued by Caspari and Jules Haag.
How to verify this yourself
Verify via Phillips' memoir in the Annales des Mines (1861); it was a publication, not a patent.
Manufacturers known to have used it
- Swiss and French precision makers
Related photographs
No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.
Sources & references
- Balance spring, Wikipedia (English), retrieved 2026-10-28 (text CC BY-SA 4.0)
- Édouard Phillips, Wikipedia (French), retrieved 2026-10-28 (text CC BY-SA 4.0)
- Phillips, É., Mémoire sur le spiral réglant (1861)
- Daniels, G., Watchmaking
Where sources disagree, the disagreement is stated rather than resolved silently.