Measurement of the Distance between the Mirrors.
Square lead weights were placed along the line, and measurements taken from the forward side of one to forward side of the next. The tape rested on the ground (which was very nearly level), and was stretched by a constant force of 10 pounds.
The correction for length of the tape (100.006) was +0.12 of a foot.
To correct for the stretch of the tape, the latter was stretched with a force of 15 pounds, and the stretch at intervals of 20 feet measured by a millimeter scale.
| At | 100 | feet the stretch was | 8.0 |
| 80 | feet the stretch was | 5.0 | |
| 60 | feet the stretch was | 5.0 | |
| 40 | feet the stretch was | 3.5 | |
| 20 | feet the stretch was | 1.5 | |
| --- | --- | ||
| 300 | 23.00 |
| Weighted mean | = | 7.7 mm. |
| For 10 pounds, stretch | = | 5.1 mm. |
| = | 0.0167 feet. | |
| Correction for whole distance | = | +0.33 feet. |
The following are the values obtained from five separate measurements of the distance between the caps of the piers supporting the revolving mirror and the distant reflector; allowance made in each case for effect of temperature:
| 1985.13 | feet. | |
| 1985.17 | feet. | |
| 1984.93 | feet. | |
| 1985.09 | feet. | |
| 1985.09 | feet. | |
| ------- | ||
| Mean = | 1985.082 | feet. |
| +.70. | Cap of pier to revolving mirror. | |
| +.33. | Correction for stretch of tape. | |
| +.12. | Correction for length of tape. | |
| -------- | ||
| 1986.23. | True distance between mirrors. |
Rate of Standard Ut3 Fork.
The rate of the standard Ut3 fork was found at the Naval Academy, but as so much depended on its accuracy, another series of determinations of its rate was made, together with Professor Mayer, at the Hoboken Institute of Technology.