As three rods were all that were necessary, the clockmaker who desired a pendulum that was compensated soon found his most easily made rod consisted of a zinc bar, wide, thin and flat, placed between two steel parts, like the meat and bread of a sandwich. This gives a flat and apparently solid rod of metal which if polished gives a pleasing appearance, and combines accurate performance with cheapness of construction, so that any watchmaker may make it himself, without expensive tools.
Fig. 9. Pendulum with compensated
rod of steel and zinc.
A, the lens-shaped bob; T P, the total length of the compensating part.
R, the upper round part of rod.
The side showing the heads of the screws is the face side and is finished. The screws 1, 2, 3, 4 hold the three pieces from separating, but do not confine the front and middle sections in their lengthwise expansion along the rod, but are screwed into the back iron section, while the holes in the other two sections are slotted smaller than the screw heads.
The holes at the lower extreme of combination 5, 6, 7, 8, 9 are for adjustments in effecting a compensation.
The pin at 10 is the steel adjusting pin, and is only tight in the front bar and zinc bars, being loose in the back bar.
O and P show the angles in the back rod, T shows the angle in the rod at the top, m shows the pin as placed in the iron and zinc sections where they have been soldered as described.