Atlantic Steam Navigation. 161 
consequence, the direct tendency of these levers, when the power 
of wind is applied to their sails, is to upset, instead of to propel 
the ship. Hence we find, practically, that when the wind in- 
_ ereases at sea, the shipmaster’s first care is to take in the top- 
sails, which is nothing more than shortening the levers upon 
which the power of wind acts. A ship going by the wind is 
capsized when the — meine Spon the’ levers is greater than 
the resistance. 
When a ship with her ail set is taken aback, she i is hurried 
stern first into the depths of the ocean from the same cause, and 
not much time given to think about it, unless the levers are short- 
ened in time, by taking in the sails, as a change in the position 
of the ship sufficiently quick, brings the acting power to bear in 
a different. direction. 
~ If the resisting power of the ship is sufficient to sustain her po- 
sition on the water, and the levers are forced beyond their strength, 
then the ship is dismasted, and left, a helpless thing, to the mercy 
of the storm.. The power ahiays acts upon vertical levers, and 
daily practice, in sailing ships, shows the danger. Ina steam 
ship, as such, the power is applied to a combination of short 
levers, acting horizontally upon the body of the ship, and in a 
direction the reverse of the power of wind upon sails, always pro- 
pelling-the ship forward, and never losing power by a collateral 
motion. 
The paddle-wheels of the British Queen are 30 feet in diam- 
eter, of course about 93 feet in circumference. The floats are 
about three feet-asunder, which will give thirty one sets of floats 
to each wheel. There are three Sened’ in a cycloidal position in 
each set, nine and a half feet in the clear in length from one side 
of the wheel to the other, and -one foot in breadth. Hence you 
will perceive that each set of floats has a superficial area of twenty 
eight and a half square feet, equal to 873 square feet for each 
wheel, and 1746 for both. The midship section of the British 
Queen presents a resistance of 550 square feet to be overcome by 
1746 feet of the floats. 
The mean speed of the wheels may be taken at sixteen revo- 
lutions per minute, and at that rate would run 29,760 yards per 
hour, equal ‘to seventeen miles. If we deduct one fifth, the usual 
Sicieaiee, from the velocity of the periphery, to reduce it to the 
mean velocity of the wheel, we then have thirteen and a_ half 
Vou. XXXV.—No. 1. 21 
