Set of determinations made at Naval Academy.
The fork was armed with a tip of copper foil, which was lost during the experiments and replaced by one of platinum having the same weight, 4.6 mgr. The fork, on its resonator, was placed horizontally, the platinum tip just touching the lampblacked cylinder of a Schultze chronoscope. The time was given either by a sidereal break-circuit chronometer or by the break-circuit pendulum of a mean-time clock. In the former case the break-circuit worked a relay which interrupted the current from three Grove cells. The spark from the secondary coil of an inductorium was delivered from a wire near the tip of the fork. Frequently two sparks near together were given, in which case the first alone was used. The rate of the chronometer, the record of which was kept at the Observatory, was very regular, and was found by observations of transits of stars during the week to be +1.3 seconds per day, which is the same as the recorded rate.
Specimen of a Determination of Rate of Ut3 Fork.
Temp.=27° C. Column 1 gives the number of the spark or the number of the second. Column 2 gives the number of sinuosities or vibrations at the corresponding second. Column 3 gives the difference between 1 and 11, 2 and 12, 3 and 13, etc.
| 1. | 0.1 | 2552.0 | |
| 2. | 255.3 | 2551.7 | |
| 3. | 510.5 | 2551.9 | |
| 4. | 765.6 | 2551.9 | |
| 5. | 1020.7 | 2552.1 | |
| 6. | 1275.7 | 2552.0 | |
| 7. | 1530.7 | 2551.8 | |
| 8. | 1786.5 | 2551.4 | |
| 9. | 2041.6 | 2551.7 | |
| 10. | 2297.0 | 2551.5 | |
| ------- | |||
| 11. | 2552.1 | 255.180 | = mean ÷ 10. |
| 12. | 2807.0 | + .699 | = reduction for mean time. |
| 13. | 3062.4 | + .003 | = correction for rate. |
| 14. | 3317.5 | + .187 | = correction for temperature. |
| ------- | |||
| 15. | 3572.8 | 256.069 | = number of vibrations per second at 65° Fahr. |
| 16. | 3827.7 | ||
| 17. | 4082.5 | ||
| 18. | 4335.9 | ||
| 19. | 4593.3 | ||
| 20. | 4848.5 |
The correction for temperature was found by Professor Mayer by counting the sound-beats between the standard and another Ut3 fork, at different temperatures. His result is +.012 vibrations per second for a diminution of 1° Fahr. Using the same method, I arrived at the result +.0125. Adopted +.012.
Résumé of determinations made at Naval Academy.
In the following table the first column gives the date, the second gives the total number of seconds, the third gives the result uncorrected for temperature, the fourth gives the temperature (centigrade), the fifth gives the final result, and the sixth the difference between the greatest and least values obtained in the several determinations for intervals of ten seconds:
| July | 4 | 20 | 255.882 | 27.0 | 256.069 | 0.07 | |
| 5 | 19 | 255.915 | 26.4 | 256.089 | 0.05 | ||
| 5 | 18 | 255.911 | 26.0 | 256.077 | 0.02 | ||
| 6 | 21 | 255.874 | 24.7 | 256.012 | 0.13 | ||
| 6 | 9 | 255.948 | 24.8 | 256.087 | 0.24 | ||
| 7 | 22 | 255.938 | 24.6 | 256.074 | 0.05 | ||
| 7 | 21 | 255.911 | 25.3 | 256.061 | 0.04 | ||
| 8 | 20 | 255.921 | 26.6 | 256.100 | 0.02 | ||
| 8 | 20 | 255.905 | 26.6 | 256.084 | 0.06 | ||
| 8 | 20 | 255.887 | 26.6 | 256.066 | 0.03 | ||
| ------- | |||||||
| Mean = | 256.072 |
In one of the preceding experiments, I compared the two Vt3 forks while the standard was tracing its record on the cylinder, and also when it was in position as for use in the observations. The difference, if any, was less than .01 vibration per second.