Round rods may be treated in the same manner, but it is usual to drill a round hole in such a rod to just fit the wire, then insert and rivet as before after the wax is cold, finishing with a ferrule or cap of brass at the end of the rod.
The slot for the suspension spring is fitted to the upper end of the rod in the same manner.
Pendulum with Shot.—Still another method of making a compensating pendulum, which gives a lighter pendulum, is to make a case of light brass or steel tubing of about three inches diameter. [Fig. 8], with a bottom and top of equal weight, so as to keep the center of oscillation about the center of gravity, for convenience in working. The bottom may be turned to a close fit, and soldered, pinned, or riveted into the tube. It is pierced at its center and another tube of the same material as the outer tube, with an internal diameter which closely fits the pendulum rod is soldered or riveted into the center of the bottom, both bottom and top being pierced for its admission and the other parts fitted as previously described.
The length of the case or canister should be about 11.5 inches so as to give room for a column of shot of 10.5 inches (the normal compensating height for lead) and still leave room for correction. Make a tubular case for the driving weight also and then we have a flexible system. If it is necessary to add or subtract weight to obtain the proper arcs of oscillation of the pendulum, it can be readily done by adding to or taking from the shot in the weight case.
Fill the pendulum to 10.5 inches with ordinary sportsmen’s shot and try it for rate. If it gains in heat and loses in cold it is over-compensated and shot must be taken from it. If it loses in heat and gains in cold it is under-compensated and shot should be added.
The methods of calculation were given in full in describing the zinc pendulum and hence need not be repeated here, but attention should be called to the fact that there are three materials here, wood, steel or brass and lead and each should be figured separately so that the last two may just counterbalance the first. If the case is made light throughout the effect upon the center of oscillation will be inappreciable as compared with that of the lead, but if made heavier than need be, it will exert a marked influence, particularly if its highest portion (the cover) be heavy, as we then have the effect of a shifting weight high up on the pendulum rod. If made of thin steel throughout and nickel plated, we shall have a light and handsome case for our bob. If this is not practicable, or if the color of brass be preferred, it may be made of that material.
The following table of weights will be of use in making calculations for a pendulum or for clock weights.
Weight of Lead, Zinc and Cast Iron Cylinders One-Half Inch Long.
| Diameter in Inches. | Weight in Pounds. | ||
|---|---|---|---|
| Lead | Zinc | Iron | |
| .25 | .020 | .012 | .012 |
| .5 | .080 | .049 | .050 |
| .75 | .180 | .111 | .114 |
| 1. | .321 | .198 | .204 |
| 1.25 | .503 | .310 | .319 |
| 1.5 | .724 | .447 | .459 |
| 1.75 | .984 | .607 | .624 |
| 2. | 1.287 | .794 | .816 |
| 2.25 | 1.630 | 1.005 | 1.033 |
| 2.5 | 2.009 | 2.239 | 1.274 |
| 2.75 | 2.434 | 1.502 | 1.544 |
| 3. | 2.897 | 1.788 | 1.837 |
| 3.25 | 3.400 | 2.098 | 2.156 |
| 3.5 | 3.944 | 2.434 | 2.491 |
| 3.75 | 4.51 | 2.783 | 2.865 |
| 4. | 5.149 | 3.177 | 3.265 |
| 4.25 | 5.813 | 3.587 | 3.686 |
| 4.5 | 6.519 | 3.922 | 4.134 |
| 4.75 | 7.265 | 4.483 | 4.607 |
| 5. | 8.048 | 4.966 | 5.103 |
| 5.25 | 8.872 | 5.474 | 5.626 |
| 5.5 | 9.737 | 6.008 | 5.175 |
| 5.75 | 10.643 | 6.567 | 6.749 |
| 6. | 11.590 | 7.152 | 7.350 |
Example:—Required, the weight of a lead pendulum bob, 3 inches diameter, 9 inches long, which has a hole through it .75 inch in diameter. The weight of a lead cylinder 3 inches diameter in the table is 2.897, which multiplied by 9 (the length given) = 26.07 lbs. Then the weight in the table of a cylinder .75 inch diameter is .18 and .18 × 9 = 1.62 lbs. And 26.07 - 1.62 = 24.45, the weight required in lbs.