Mr William Galbraith on the Tides and Dew-Point. 17 
pretty conformable to the best hygrometric instruments. The ther- 
mometers used were made by my friend, Mr John Adie, optician. 
New Formula. 
Let f’ represent the force of aqueous vapour at the dew-point. 
Ff, the force of aqueous vapour, at the temperature of eva- 
poration. 
r, the temperature by the dry thermometer. 
t, that by the thermometer with the wet bulb. 
+ — t = 6¢, the difference of these two; 
And 6, the height of the barometer, then 
Ff =f — b (0:000356 + 0:0000005 ¢) 6t it? pero a Goer 
Where the value of f’ will give, by a table of the force of aqueous 
vapour at different temperatures, such as that in my Mathematical 
Tables, page 64, Table IV., or that of Dalton, the corresponding 
dew-point. 
1st, f/ = 0-4817 — 30-2 (0:000356 + 0:0000005 x 581°) 5:7". 
Or f = 0°4817 — 0:0663 = 0°4154, which, by the table, gives 
d the dew-point at 53°°8 Fah., and so on “wit the others as in the 
following table :— 
Table of Results from the preceding Formula in August 1849. 
iz | 
| No. Date. ~ Time. Nero mee Barometer. Dew-Foints) 
H. M. 2 | 2 In | 
1 | Aug. 6,| 10°O04m. | 6383 | 581 30:20 | 53:8 
2 | 6,| 650 pm.| 640 | 560 30°20 48°6 
3 | 7, | 11°40 am 60°0 57°6 30°10 55:2 
4 8, | 0°45 pm 65:0 | 62:0 30:00 601 
| 5 8, | 4°45 pm 68:0 64:0 29°80 61:6 
| 6 10, | 11:0 a.m 650 | 62:0 29°80 6071 
| 7 | 10,|- 7-0 rm. | 640 | 61:0 29°75 | 591 
| 8 10, 9-0 Pm 66°5 63-0 20°75 61-7 
9 11, Great rain from 5 a.m. till late. 
10 13, 590 | 574 | 29°50 | 563 
11 17, 62-0 54:0 | 30:10 | 51:3 
| 12 18,| 5°30 p.m. | 565 | 50°0 30°20 44:0 
| 13 20, SOam. | 59:0 | 56:0 | 30°30 | 55°3 
| Weather wet. | | 
In this way it is hoped I have shewn how a number of interesting 
results may be obtained by a little diligence and attention, with very 
VOL. XLVIII. NO. XCV.—JAN. 1850. B 
