An expression for the period of a conical Jolly balance spring is deduced theoretically and the result is verified by experimental data. By some assumptions which simplify the equation of motion it is reduced to that for simple harmonic motion from which the period is obtained.
R. B. ABBOTT, "PERIOD OF A LOADED CONICAL JOLLY BALANCE SPRING," J. Opt. Soc. Am. 17, 318-322 (1928)