| 256.180 | |
| 256.036 | |
| 256.072 | |
| 256.068 | |
| ------- | |
| Mean = | 256.089 |
The previous work was omitted on account of various inaccuracies and want of practice, which made the separate results differ widely from each other.
The Formulæ.
The formulæ employed are—
| d′ | |
| (1) tan φ = | ----- |
| r | |
| 2592000″ × D × n | |
| (2) V = | ----------------- |
| φ″ | |
| φ = | angle of deflection. |
| d′ = | corrected displacement (linear). |
| r = | radius of measurement. |
| D = | twice the distance between the mirrors. |
| n = | number of revolutions per second. |
| α = | inclination of plane of rotation |
| d = | deflection as read from micrometer. |
| B = | number of beats per second between electric Vt₂ fork and standard Vt3 |
| Cor = | correction for temperature of standard Vt3. |
| V = | velocity of light. |
| T = | value of one turn of screw. (Table, page 126.) |
Substituting for d, its value or d×T×sec α (log sec α = .00008), and for D its value 3972.46, and reducing to kilometers, the formulæ become—
| dT | |||
| (3) tan φ = | c′ | ----; | log c′ = .51607 |
| r | |||
| n | |||
| (4) V = c ---; | log c = .49670 | ||
| φ | |||
| D and r are expressed in feet and d′ in millimeters. | |||
| Vt3 fork makes 256.070 vibrations per second at 65° Fahr. | |||
| D = | 3972.46 feet. | ||
| tan α = | tangent of angle of inclination of plane of rotation = 0.02 in all but the last twelve observations, in which it was 0.015. | ||
| log c′ = | .51607 (.51603 in last twelve observations.). | ||
| log c = | .49670. | ||
The electric fork makes ½(256.070 + B + cor.) vibrations per second, and n is a multiple, submultiple, or simple ratio of this.