1815.) the Rise and Fall of the Tide. 279 
Column | contains the velocity of the plane in feet per second. 
Column 2 contains columns of water, the base of each of which 
was one square foot, and the respective altitude equal to the space 
through which a body must fall to acquire the velocity of one, two, 
three, four,. five, six, &c. feet per second. 
Column 3 contains the weights of the different columns of water 
in pounds avoirdupois. 
Column 4, the resistance to the plane by experiment. 
Column 5, the plus pressure found by subtracting the minus 
pressure contained in column 6th from the total resistance set down 
in column 4th. 
Column 6, the minus pressure found by experiment. 
Column 7, the difference between the calculated resistances con- 
tained in column 3d and the plus pressure in column 5th. 
Column 8, the exponents of the minus pressure ; and in the last 
horizontal column the exponents of the total resistances and plus 
pressure. 
Wind, it appears by table Ist, when moving with a velocity of 
20 feet in a second, exerts a force on a square foot placed at right 
angles to its direction equal to 13°567 ounces; and water, by table 
2d, when running one foot per second, acts on the same surface, 
similarly placed, a power equal to 1°2949 Ibs. or 20°718 oz. To 
find the velocity water must have to produce equal effect with wind, 
Vm:um::R:7, V beisg equal to one foot or !2 inches, 7 to 
13°567 oz., K to 20°718 oz,, and the exponent m to 1°9243, whence 
r is 9°6301 inches, the required velocity. Then eine is equal to 
24'922, the celerity of tae wind to produce the same effect as water; 
d 20°718 
ane 9319 
with equal velocity, wind has nearly 650 part less power than water. 
As air is 860 times lighter than water, and supposing the velocity of 
water to be 1, and the resistance as the square of the velocity V = 
860 = 29°326, which by no means accords with the result de- 
duced from experiment, and the effect of air in lieu of —+. part is 
ats: Experiment also proves that the most advantageous angle for 
the sail of a windmill to be set in motion in is 60°, instead of 35° 
16’, reckoning from the plane of its motion, or the wind should 
strike the sail at an angle of 30°, and not 54° 44’; and the most 
advantageous angle for the rudder to make with the keel, when the 
impulse of the water is given, I believe to be 30°. After the im- 
adie is given, and the vessel turns, the angle should be altered, if 
the rudder coincides with the curve described by the stern, because 
then it is evident the rudder would be of no use. 
In the Examen Maritime by Don Georges Juan, traduit de 
Espagnol, the resistance of fluids is supposed to be, as their den- 
sities, as the surface opposed to their action, and as the square root 
of the depth to which the opposing obstacle is immersed. ‘That the 
first supposition is not well founded, will, I think, appear from the 
gives 649°48: consequently if wind and water move 
