456 
MR. BAILY ON THE CORRECTION OF 
It appears then that all these results accord with the theory that a quantity 
of air adheres to every pendulum when in motion: and, by thus forming a 
portion of the moving body, diminishes its specific gravity; or, rather adds to 
its inertia. This adhesive air is confined almost wholly to the two opposite 
portions of the pendulum, which lie in the line of its motion ; (similar to what 
takes place with a body moving through still water), and very little of it ad¬ 
heres to, or is dragged by, the sides of the pendulum. The shape of this coat¬ 
ing of air will consequently partake, in some measure, of the form of the pen¬ 
dulum ; subject probably to some slight modifications, with the nature of 
which, however, we are at present unacquainted. The quantity of air dragged 
by a pendulum seems to depend on the extent and form of surface opposed to 
its action, and is not affected by the density of the body. 
In the case of a sphere , 1 inch in diameter, suspended by a fine wire, the 
weight of air dragged by the sphere alone appears to be about 0T23 grain 
troy: and for spheres of any other diameter, in nearly the direct ratio of the 
cubes of their diameters. The weight of air dragged by the wire (of the length 
of the seconds pendulum), may amount to 0T0 grain, but probably does not 
exceed that quantity; and perhaps is nearly constant for all jine wires of that 
length : so that with small spheres (less than 1 inch in diameter), the weight 
of air dragged by the wire , is nearly the same as that dragged by the sphere. 
With respect to cylinders suspended by rods, and swung with their flat sides 
opposed to the line of motion, the law of the variation is not so manifest; as 
we are at present ignorant of the precise effect caused by the edge of the cylin¬ 
der. Neither have we obtained sufficient data to develope the effect of the air 
on cylinders, suspended by rods or wires, and swung with their flat sides in a 
horizontal position; similar to the pendulums No. 10 and 14. In these cases 
(see page 433), the 4 inch cylinder drags much more than double the quantity 
of air adhering to the 2 inch cylinder: although they have precisely the same 
diameter. And these are the only experiments, which I have made, connected 
with this branch of the subject. 
With respect to very thin cylinders, or discs, swung with their flat sides 
opposed to the line of motion, the weight of air dragged by a disc, of 1 inch 
in diameter, appears to be about 0T49 grain; and for discs of any other dia¬ 
meter, nearly in the direct ratio of the cubes of their diameters. Whence it 
appears that a thin disc drags more air than a sphere of the same diameter. 
