Example: Altitude of Barometer above sea level, 205 feet; Temperature of the air, 45°; Correction = ?
Here 205 feet and 45° are neither of them found in the table. Hence a double interpolation is necessary. For 200 feet and 40° the correction is +.224 inch. For 200 feet and 50° the correction is +.220 inch. Hence for 200 feet and 45° the correction is +.222 inch. For 210 feet and 40° the correction is +.235 inch. For 210 feet and 50° the correction is +.231 inch. Hence for 210 feet and 45° the correction is +.233 inch. Now for 205 feet we should have a correction midway between +.235 inch and +.233 inch or +.234 inch.
Table I.—Temperature of the Dew-Point, in Degrees Fahrenheit.
| t | Difference between the dry and wet thermometers (t-t′) | t | ||||||||||||
| (Dry ther.) | 0°.2 | 0°.4 | 0°.6 | 0°.8 | 1°.0 | 1°.2 | 1°.4 | 1°.6 | 1°.8 | 2°.0 | 2°.2 | 2°.4 | 2°.6 | (Dry ther.) |
| -40 | -52 | -40 | ||||||||||||
| -39 | -50 | -39 | ||||||||||||
| -38 | -49 | -38 | ||||||||||||
| -37 | -48 | -37 | ||||||||||||
| -36 | -46 | -36 | ||||||||||||
| -35 | -44 | -35 | ||||||||||||
| -34 | -43 | -58 | -34 | |||||||||||
| -33 | -42 | -55 | -33 | |||||||||||
| -32 | -40 | -52 | -32 | |||||||||||
| -31 | -38 | -49 | -31 | |||||||||||
| -30 | -36 | -47 | -30 | |||||||||||
| -29 | -35 | -44 | -29 | |||||||||||
| -28 | -33 | -42 | -56 | -28 | ||||||||||
| -27 | -32 | -40 | -52 | -27 | ||||||||||
| -26 | -30 | -37 | -48 | -26 | ||||||||||
| -25 | -29 | -35 | -45 | -25 | ||||||||||
| -24 | -28 | -34 | -43 | -58 | -24 | |||||||||
| -23 | -27 | -32 | -40 | -53 | -23 | |||||||||
| -22 | -26 | -30 | -37 | -49 | -22 | |||||||||
| -21 | -25 | -29 | -35 | -45 | -21 | |||||||||
| -20 | -23 | -28 | -33 | -41 | -55 | -20 | ||||||||
| -19 | -22 | -26 | -31 | -38 | -50 | -19 | ||||||||
| -18 | -21 | -25 | -29 | -35 | -45 | -18 | ||||||||
| -17 | -20 | -23 | -27 | -32 | -41 | -55 | -17 | |||||||
| -16 | -19 | -22 | -26 | -30 | -37 | -49 | -16 | |||||||
| -15 | -17 | -20 | -24 | -28 | -34 | -44 | -15 | |||||||
| -14 | -16 | -19 | -22 | -26 | -31 | -39 | -52 | -14 | ||||||
| -13 | -15 | -18 | -21 | -25 | -29 | -35 | -46 | -13 | ||||||
| -12 | -14 | -17 | -20 | -23 | -27 | -32 | -41 | -55 | -12 | |||||
| -11 | -13 | -16 | -18 | -21 | -25 | -30 | -36 | -48 | -11 | |||||
| -10 | -12 | -14 | -17 | -20 | -23 | -27 | -33 | -42 | -58 | -10 | ||||
| -9 | -11 | -13 | -15 | -18 | -21 | -25 | -30 | -37 | -48 | -9 | ||||
| -8 | -10 | -12 | -14 | -17 | -20 | -23 | -27 | -33 | -42 | -58 | -8 | |||
| -7 | -9 | -11 | -13 | -15 | -18 | -21 | -25 | -30 | -36 | -48 | -7 | |||
| -6 | -8 | -10 | -12 | -14 | -16 | -19 | -23 | -27 | -32 | -41 | -56 | -6 | ||
| -5 | -7 | -8 | -10 | -12 | -15 | -17 | -21 | -24 | -29 | -35 | -47 | -5 | ||
| -4 | -6 | -7 | -9 | -11 | -13 | -16 | -19 | -22 | -26 | -31 | -39 | -54 | -4 | |
| -3 | -4 | -6 | -8 | -10 | -12 | -14 | -17 | -20 | -23 | -28 | -33 | -44 | -3 | |
| -2 | -3 | -5 | -6 | -8 | -10 | -12 | -15 | -18 | -21 | -24 | -29 | -36 | -48 | -2 |
| -1 | -2 | -4 | -5 | -7 | -9 | -11 | -13 | -16 | -18 | -22 | -26 | -31 | -39 | -1 |
| ±0 | -1 | -3 | -4 | -6 | -7 | -9 | -11 | -14 | -16 | -19 | -23 | -27 | -33 | 0 |
| +1 | -0 | -2 | -3 | -4 | -6 | -8 | -10 | -12 | -14 | -17 | -20 | -24 | -28 | +1 |
| 2 | +1 | -1 | -2 | -3 | -5 | -6 | -8 | -10 | -12 | -15 | -17 | -21 | -25 | 2 |
| 3 | 2 | +1 | -1 | -2 | -3 | -5 | -7 | -8 | -10 | -13 | -15 | -18 | -21 | 3 |
| 4 | 3 | +2 | 0 | -1 | -2 | -4 | -5 | -7 | -9 | -11 | -13 | -16 | -19 | 4 |
| 5 | 4 | 3 | +1 | 0 | -1 | -2 | -4 | -5 | -7 | -9 | -11 | -14 | -16 | 5 |
| 6 | 5 | 4 | 3 | +1 | 0 | -1 | -3 | -4 | -6 | -7 | -9 | -12 | -14 | 6 |
| 7 | 6 | 5 | 4 | 3 | +1 | 0 | -1 | -3 | -4 | -6 | -8 | -10 | -12 | 7 |
| 8 | 7 | 6 | 5 | 4 | 3 | +1 | 0 | -1 | -3 | -4 | -6 | -8 | -10 | 8 |
| 9 | 8 | 7 | 6 | 5 | 4 | 3 | +1 | 0 | -1 | -3 | -4 | -6 | -8 | 9 |
| 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | +1 | 0 | -1 | -3 | -4 | -6 | 10 |
| 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | +2 | 0 | -1 | -3 | -4 | 11 |
| 12 | 11 | 10 | 9 | 9 | 8 | 7 | 5 | 4 | 3 | +2 | 0 | -1 | -2 | 12 |
| 13 | 12 | 11 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 3 | +2 | +1 | -1 | 13 |
| 14 | 13 | 12 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 2 | +1 | 14 |
| 15 | 14 | 13 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 15 |
| 16 | 15 | 15 | 14 | 13 | 12 | 11 | 10 | 10 | 9 | 8 | 7 | 5 | 4 | 16 |
| 17 | 16 | 16 | 15 | 14 | 13 | 12 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 17 |
| 18 | 17 | 17 | 16 | 15 | 14 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 18 |
| 19 | 18 | 18 | 17 | 16 | 15 | 15 | 14 | 13 | 12 | 11 | 10 | 10 | 9 | 19 |
| 20 | 19 | 19 | 18 | 17 | 17 | 16 | 15 | 14 | 13 | 13 | 12 | 11 | 10 | 20 |
| t. | 0°.2 | 0°.4 | 0°.6 | 0°.8 | 1°.0 | 1°.2 | 1°.4 | 1°.6 | 1°.8 | 2°.0 | 2°.2 | 2°.4 | 2°.6 | t. |
Table I.—Temperature of the Dew-Point, in Degrees Fahrenheit.
| t | Difference between the dry and wet thermometers (t-t′). | t | |||||||||
| (Dry ther.) | 2°.6 | 2°.8 | 3°.0 | 3°.2 | 3°.4 | 3°.6 | 3°.8 | 4°.0 | 4°.2 | 4°.4 | (Dry ther.) |
| -2 | -48 | -2 | |||||||||
| -1 | -39 | -54 | -1 | ||||||||
| 0 | -33 | -43 | 0 | ||||||||
| +1 | -28 | -35 | -46 | +1 | |||||||
| 2 | -25 | -30 | -37 | -50 | 2 | ||||||
| 3 | -21 | -26 | -31 | -39 | -54 | 3 | |||||
| 4 | -19 | -22 | -27 | -32 | -42 | -60 | 4 | ||||
| 5 | -16 | -19 | -23 | -28 | -34 | -45 | 5 | ||||
| 6 | -14 | -17 | -20 | -24 | -29 | -35 | -47 | 6 | |||
| 7 | -12 | -14 | -17 | -20 | -24 | -29 | -37 | -50 | 7 | ||
| 8 | -10 | -12 | -15 | -17 | -21 | -25 | -30 | -38 | -53 | 8 | |
| 9 | -8 | -10 | -12 | -15 | -18 | -21 | -25 | -31 | -39 | -55 | 9 |
| 10 | -6 | -8 | -10 | -12 | -15 | -18 | -21 | -26 | -31 | -40 | 10 |
| 11 | -4 | -6 | -8 | -10 | -12 | -15 | -18 | -21 | -26 | -31 | 11 |
| 12 | -2 | -4 | -6 | -8 | -10 | -12 | -15 | -18 | -21 | -26 | 12 |
| 13 | -1 | -2 | -4 | -5 | -7 | -9 | -12 | -14 | -17 | -21 | 13 |
| 14 | +1 | 0 | -2 | -3 | -5 | -7 | -9 | -11 | -14 | -17 | 14 |
| 15 | 3 | +1 | 0 | -2 | -3 | -5 | -7 | -9 | -11 | -14 | 15 |
| 16 | 4 | 3 | +2 | 0 | -1 | -3 | -4 | -6 | -8 | -10 | 16 |
| 17 | 6 | 5 | 3 | +2 | +1 | -1 | -2 | -4 | -6 | -8 | 17 |
| 18 | 7 | 6 | 5 | 4 | 2 | +1 | 0 | -2 | -3 | -5 | 18 |
| 19 | 9 | 8 | 7 | 5 | 4 | 3 | +1 | 0 | -1 | -3 | 19 |
| 20 | 10 | 9 | 8 | 7 | 6 | 5 | 3 | +2 | +1 | -1 | 20 |
| t. | 2°.6 | 2°.8 | 3°.0 | 3°.2 | 3°.4 | 3°.6 | 3°.8 | 4°.0 | 4°.2 | 4°.4 | t. |
| t. | 4°.6 | 4°.8 | 5°.0 | 5°.2 | 5°.4 | 5°.6 | 5°.8 | 6°.0 | 6°.2 | 6°.4 | t. |
| 8 | 8 | ||||||||||
| 9 | 9 | ||||||||||
| 10 | -57 | 10 | |||||||||
| 11 | -41 | -60 | 11 | ||||||||
| 12 | -31 | -41 | -59 | 12 | |||||||
| 13 | -25 | -31 | -40 | -58 | 13 | ||||||
| 14 | -20 | -25 | -30 | -39 | -56 | 14 | |||||
| 15 | -16 | -20 | -24 | -30 | -38 | -53 | 15 | ||||
| 16 | -13 | -16 | -19 | -23 | -28 | -36 | -50 | 16 | |||
| 17 | -10 | -12 | -15 | -18 | -22 | -27 | -34 | -47 | 17 | ||
| 18 | -7 | -9 | -12 | -14 | -17 | -21 | -26 | -32 | -44 | 18 | |
| 19 | -5 | -7 | -9 | -11 | -14 | -17 | -20 | -25 | -30 | -40 | 19 |
| 20 | -2 | -4 | -6 | -8 | -10 | -13 | -16 | -19 | -23 | -29 | 20 |
| t. | 4°.6 | 4°.8 | 5°.0 | 5°.2 | 5°.4 | 5°.6 | 5°.8 | 6°.0 | 6°.2 | 6°.4 | t. |
Table I.—Temperature of the Dew-Point, in Degrees Fahrenheit.