of Bodies moving in Fluids. 5 
agreed so nearly, that there can be no doubt but that they give 
the actual resistance to a very considerable degree of accuracy. 
In our experiments, the planes were immersed at some depth 
in the fluid ; in the other case, the bodies floated on the surface ; 
and I can see no way of accounting for the difference of the 
resistances, but by supposing that, at the surface of the fluid, 
the fluid from the end of the body may escape more easily 
than when the body is immersed below the surface ; but this, 
I confess, appears by no means a satisfactory solution of the 
difficulty. The resistances of bodies descending in fluids mani- 
festly come under the case of our experiments. 
Two semi-globes were next taken, and made to revolve with 
their flat sides forwards. The diameter of each was 1,1 in. the 
distance of the centre of resistance from the axis was 6,2 2 in. 
and they moved with a velocity of 0,542 feet in a second ; and 
the resistance was found to be 0,08339 oz. by experiment. By 
theory, the resistance is 0,05496 oz. ; hence, the resistance by 
experiment : the resistance by theory : : 0,08339 : 0,05496, 
agreeing very well with the abovementioned proportion. But, 
when the spherical sides moved forwards with the same velo- 
city, the resistance was 0,034 oz - Hence, the resistance on 
the spherical side of a semi-globe : resistance on its base :: 
0,034 : 0,08339; but this is not the proportion of the resist- 
ance of a perfect globe to the resistance of a cylinder of the 
same diameter, moving with the same velocity, because the 
resistance depends upon the figure of the back part of the 
body. 
I therefore took two cylinders, of the same diameter as the 
two semi-globes, and of the same weight; and, giving them 
the same velocity, I found the resistance to be 0,07938 oz. ; 
a ' 
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1 
