16 Mr William Galbraith on the Tides and Dew-Point. 
Barometrical observations, . ; . 29°25 inches. 
Reduction from 64° to 50° Fahr., : . —"05 
Barometer at 50° Fahr. > : . . 29:20 
Standard barometer, . 2 ; é . 30°00 
Deficit, . : : : d : Sees) 
Hence the correction = +11 x 0°8=0°88 foot and 3-50 + 0°88 
= 4-38 feet, the depression of the tide under the pier after allowing 
for the state of the barometer and thermometer. But, according to 
the best estimation I can deduce from a consideration of the cireum- 
stances of the case, the depression would have been about 5°40 or 
5-50 feet. Hence 5:-45—4:38=1°07 foot, the effect of the wind 
upon the tide. If, however, experiments were made with a register 
tide-gauge, combined with a wind-gauge, the exact quantity of rise 
caused by the state of the barometer and winds respectively, could 
be accurately determined. ‘Till these machines are erected in all 
eligible places round our coasts, there will always be much uncer- 
tainty in the time and height of the tides. 
What I have here said is, I fear, far from satisfactory to the 
public, who take an interest in these matters ; and I freely admit, 
from the inadequacy of my means, it is not much so to myself. It 
may, however, be the means of drawing attention to this most inte- 
resting subject, especially to a maritiine country like this, whose in- 
terests are so much involved in trade and commerce. 
It may also be inferred that the greatest rise of the tide by our 
observations was 8°68 feet on 4th August 1849, near full moon; 
and one-half of this, or 4°34 feet is the unit wu of the height 
of the tide above the mean level of the sea, as understood by Laplace, 
&c., and explained in the new edition of Ainslie’s Surveying, page 
398, while that of the neaps is about 3-36 feet, and the establish- 
ment is near noon, Greenwich, mean time, or 11" 34™, Broddick, 
apparent time. 
TI. On the Dew-Point. 
Another interesting subject is the determination of the dew- 
ing point, that is, the temperature at which, in a given atmosphere, 
dew will be deposited from it on material objects. ~Daniell’s Hygro- 
meter is a very convenient, though rather an expensive, instrument 
for this purpose. It has therefore been an object with many to de- 
termine this with simpler and less expensive instruments. Accord- 
ingly, two thermometers have been repeatedly proposed for this pur- 
pose, one whose bulb is covered with wet cloth, and another dry and 
uncovered. After a good many experiments and attempts with 
various success, I have found the following formula to give results 
