253 
Mr T. Tredgold on Steam-Boats. 
be changed to suit the circumstances, this will be the best pro- 
portion for all cases. Where the force of a current is consider- 
able, it would be extremely desirable to have the pow r er of alter- 
ing the velocity of the wheels ; and it is not proper that it should 
be done by any change in the velocity of the steam-piston ; be- 
cause, whatever change is made in its velocity, must affect the 
power of the engine. There is no difficulty in adopting such a 
train of mechanism as w T ould produce the alteration of velocity 
required, and yet be as strong and durable as the ordinary com- 
bination, and not at all expensive, compared with the object to 
be gained by introducing it. It will only be necessary to pro- 
vide for an increase of velocity ; for, when the boat goes with the 
stream, the rate of the paddles is already too great ; whereas, 
when a boat moves against the current, both an increase of ve- 
locity of the wheel, and an increase of surface of paddle, is neces- 
sary, to maintain the mean rate. 
I will close this paper with a view of the velocity a boat may 
be expected to acquire, when the power is the same. Let P be 
the power of the engine, then ^ = P. 
Put the ratio of the velocity of the current to the velocity of 
the boat, as 1 : n ; that is, 1 : n : : v : c — n v ; whence we have 
+ = P) or 
u 2 5 
\a (1 _ 4 _ nY / 
(1 - 4 - n)‘ 
If the boat moves in a current of which the velocity is n times 
the velocity of the boat, then we shall have 
Velocity of Current. 
With the stream, 4 miles per hour. 
2*2 
1*53 
Still water, - 0*00 — — 
Against the stream, 1-08 
1- 38 
1*92 — - 
2- 38 
3*17 
Velocity of Bout. 
8 miles per hour. 
6*6 
6-12 
5.00 - — - 
4-34 
4.16 
3*85 
3*58 
3*17 
This Table shews, that a power capable of moving a boat at 
the rate of five miles per hour, in still water, will only move it 
VOL. XIII. NO. 26 . OCTOBER 1825. 
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