290 On the intended Exeter Steam- Boat: 
Thames advertised perfect security to their passengers) under 
the new law) 4n the morning, and kept their word by blowing up 
in the evening, when ouly the crew were injured. 
Your correspondent has fairly stated the advantages likely to 
result from his plan of placing the wheels of his proposed steam- 
vessel at the stern;—but practically I fear he will find it subject 
so some disadvantages. In the first place, wheels placed at the 
stern will not impel a vessel with equal effect with wheels placed 
on each side. 2dly, Whenever the wind -is strong on either 
bow the head of the vessel will not at times obey the helm, with 
the due action of which wheels at the stern are likely to inter- 
fere. 3dly, If the wind is strong and fair, the pitching of the 
vesse] and the roll of the sea aft, will more seriously disturb the 
action of the wheels than if they were placed at or near midships. 
Presuming that it is intended to use the wheels in ordinary use, 
it would be easy for me to prove the truth of the foregoing ob- 
servation ;—but I wish to be brief, and avoid detail as much as 
possible. My object is not to damp the spirit of enterprise, but. 
to direct it as far as the case will admit into a safe and profit- 
able channel; and if your correspondent is determined to follow 
up his plan of using two wheels at the stern, I would beg leave 
to recommend him a particular construction of wheels, which ? 
invented and used many years ago, and which will materially 
assist his purpose and obviate in a great degree the objections I 
have started. The paddles of the wheels I allude to when at rest, 
present their edges in a line with the keel of the vessel; of course 
they expose little surface to the direct action of the wind or sea: 
When made to revolve, a simple but efiectual contrivance obliges 
each paddle as it successively enters the water to gradually pre- 
seut its full surface thereto, and consequently to rise out of the 
water on its edge; each paddle may therefore be considered a 
vertical rotatory feathering oar, free from all shock in entering 
the water, obtaining the full effect therefrom, and rising out 
without any lift thereof. But as the degree of obliquity of each, 
and every paddle, may be varied ina moment at pleasure; it fol- 
lows, that a vessel may be both gmpelled and steered by such 
wheels; and in place of the horizontal rudder, these rotatory 
impelling rudders might be used with advantage in every steam- 
boat, either as a substitute for, or in addition to, wheels placed 
at the sides. When so posited, the general arbor, instead of 
projecting as customary three or four feet on each side of the 
vessel, need only project half that space; and as there is no lift 
of water, no casing is necessaiy over them, the mechanism is 
boxed in and secure from all external injury, is not liable to be 
deranged, and works with very little friction. : 
A little reflection will show that these rotatory rudders might 
furnish 
