308. MARITIME OBSERVATIONS, 
ference of wheels to be turned conftantly on each fide of 
the veflel; but this method, though frequently tried, has 
never been found fo effectual as to encourage a continuance 
of the practice. I do not know that the reafon has hither- 
to been given. Perhaps it may be this, that great part of 
the force employed contributes little to the motion. For 
inftance, (fig. 12.) of the four paddles a, b, c, d, all under 
water, and turning to move a boat from X to Y, c has the 
moft power, b nearly though not quite as much, their 
motion being nearly horizontal ; but the force employed 
in moving a, is confumed in prefling almoft downright 
upon the water till it comes to the place of b; and the 
force employed in moving d is confumed in lifting the 
water till d arrives at the furface; by which means much 
of the labour is loft. It is true, that by placing the wheels 
higher out of the water, this wafte labour will be diminifh- 
ed in a calm, but where a fea runs, the wheels muft un- 
avoidably be often dipt deep in the waves, and the turn- 
ing of them thereby rendered very laborious to little 
purpofe. | 
Among the various means of giving motion to a boat, 
that of M. Bernoulli appears one of the moft fingular, 
which was to have fixed in the boat a tube in the form of 
an L, the upright part to have a funnel-kind of opening 
at top, convenient for filling the tube with water; which 
defcending and paffing through the lower horizontal part, 
and iffuing in the middle of the ftern, but under the fur- 
face of the river, fhould pufh the boat forward. There 
is no doubt that the force of the defcending water would 
have a confiderable effet, greater in proportion to the 
height from which it defcended ; but then it is to be confi- 
dered, that every bucket-full pumped or dipped up into 
the boat, from its fide or through its bottom, mutt have its 
vis inertie overcome fo as to receive the motion of the 
boat, before it can come to give motion by its defcent; 
and that will be a dedudtion from the moving power. 
To 
