I am about to build a grandfather clock using a Hermle movement and need to select a pendulum. Is there any advantage in using a lyre pendulum, as opposed to a "plain" pendulum with a single metal rod? ie. is the lyre style used purely for aesthetic appeal, or do the multiple rods on the lyre pendulum aid in compensating for length variation with temperature fluctuations?
Generally the modern lyre pendulum is in place for, as you say, aesthetic appeal. Rarely one comes across one made up with compensating rods of different expansion and contraction weight combined in such manner as to pretty much negate the atmosphere actually altering the pendulum length, thereby the speed of the clock. They are expensive. Actually if you are seeking accuracy, go to a wooden pendulum rod. In my opinion they look better anyway.