230 Instrument to measure and register {Ocr. 
experiments stated: and that the third supposition is not, is evident 
from the following experiment. ‘The plus and minus resistance of 
a parallelopipedon one foot square immersed to the depth of very. 
nearly six inches, and moving with a velocity of 12 feet in a second, 
is 152-62 lbs. avoirdupois; and in table 2d, the resistance of a plane 
containing one superficial foot immersed to the depth of six feet, 
and moving with a velocity of 12 feet, is 157°20 lbs., which is not 
widely different ; and this variation of 4:58 lbs. may partly be attri- 
buted to the longer body being less resisted than the plane. 
The first column of the following table contains the velocity in 
feet per second; and the second column contains the friction of 
water against 100 superficial feet of wood immersed to the depth of 
six feet; and great pains were bestowed in rendering the surface of 
the wood as even and smooth as possible. . ; 
The third column contains the increase of the friction by sinking 
the surface one foot lower. If the friction be required for nearer 
the surface than six feet, the numbers in this line must be subtracted 
from those in the first line ; but if lower be wanted, the numbers 
in this line must be added. ‘These numbers were determined from 
actual experiment. 
By this table a judgment may he formed what is the friction of 
the water on the bottom of a large ship; or, more properly speak- 
ing, what is the minimum of the friction ; for it is almost imprac- 
ticable to render the immersed part of any vessel so even on the 
surface as that with which the experiment was made. 
A second rate man-of-war has 15,000 superficial feet immersed 
under the water, if the draft of water be 24 feet. Supposing the 
vessel sails at the rate of 20 feet per second, and that the friction is 
calculated at the depth of 12 feet, or half the draft of water, then 
32186 + 24-668 = 146-53, which, multiplied by 150, gives 
21979 lbs. or somewhat more than nine tons ; but in fact this addi- 
tional resistance to the division of the fluid must be far greater, as 
a vessel when coppered is, comparatively speaking, a very uneven 
surface ; and any contrivance to diminish the friction would be very 
desirable. Rolled or milled copper sheets being smoother than those 
hammered, if one of his Majesty’s ships had one side coppered in 
the usual manner, and the other side with rolled or milled coppers 
pains being taken to lay the sheets on as evenly as possible, and the 
heads of the nails countersunk ; if this vessel so prepared were sent 
to sea in company with another, and under favourable circumstances, 
the two vessels, by setting more or less on the same tack, had equal 
progressive velocity ; and the two vessels put about, and run on the 
ether tack with the same quantity of sail; the difference of the 
sailing will show the advantage of the two modes of coppering. 
