28 Dec. 1998 Rock the Boat comments have reached the astounding number of six; see pages 2 & 3. These are meant to be comments no longer than half a page on horological topics, including controversial ones, but not personal. A quick way to write a short article, convey an important idea or ask a question.

Page Contents

1 Index of this issue.

2 A review of two important articles by Bryan Mumford in the November and December issues of the Horological Journal, the first is on Pendulums Interfere With Each Other (Nov.), the second is Experimental Electromagnetic Clocks. Looking ahead, Bryan will have an article in the 1999-2 issue of the HSN: Using a GPS Receiver to measure precision pendulums, the device he used in the first of the above HJ articles.

3-4 Rock the Boat: Michael Payne, Thoughts on pendulum stiffness. Carl Rozycki, a comment. Bill Ward, Supplies (mirrors, invar). Alan Heldman, more on Q. Ned Bigelow, old brass mainsprings. Ted Wale, old Atmos clock repair.

5 A unique water clock: Why Does This Pendulum Work? by Alan Heldman

6-17 Sinusoidal Drive of a Pendulum by Robert Matthys. Bob compares past designs of sinusoidal drives and discusses various flaws, *including wave clipping. He devises a circuit by means of a servo and a thermallyoperated multiplier which meets his criteria. He concludes that it is satisfactory for intermediate accuracy but not for high accuracy because it provides drive over the entire pendulum swing, including at each end.

18-21 A Useful Tool for Horological Modeling by Bob Holmstrom. Bob describes a commercially-available program that models mechanical systems. He demonstrates this by using a pendulum as an example. In addition, he takes up the question of a flexible "rope" pendulum rod (see George Feinstein's question about a flexible rod *in HSN 1998-5, and Michael Payne's discussion in the issue under "Rock the Boat'). Bob finds that the flexible rod is satisfactory as long as the geometry or forces do not create moments.

22-27 Alan Heldman writes A Venture Into the Turbulent Waters of Chaos Theory as it Pertains to Pendulums. This is a non- mathematical review of the various books on the topic as well as discussion of the terminology used.

E.C. Martt

Above: Drawing from Apians Cosmographicus Liber of 1533, showing how a nocturnal is used to tell the time at night from the Great Bear.

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