440 
MR. BAILY ON THE CORRECTION OF 
the rod. But, I have been favoured by Professor Airy with the following in¬ 
vestigation and remarks on this subject, which will clear up these and other 
seeming discordancies. 
“ It appears that the phenomena, to which you allude, may generally be ex- 
“ plained by supposing a quantity of air, depending on the figure of the body, 
“ to adhere to it whilst it is moving, and to add to its inertia without altering 
“ its gravitation. In the experiments on bodies of a simple shape, the quan- 
“ tity of air is found, whose inertia, supposing it to adhere to the centre of 
“ gyration, would account for the retardation of the pendulum (see page 431). 
“ If then a compound body C consist of two parts A and B, (the distances of their 
“ centres of gyration from the axis of motion being respectively c, a, b,) and if 
“ the air adhering to the centres of gyration of A and B respectively were a 
“ and /3 ; then the compound pendulum C must be supposed loaded with the 
“ inertia of a at the distance a, and of (3 at the distance b. The effect of these 
“ would be the same as if the inertia of 
a a~ 
+ /3 b 2 
were applied at the distance 
“ c. If then we find, as the result of experiment with the compound pendulum 
“ C, that it has (from the action of the air) the inertia y adhering to its centre 
“ of gyration, we obtain the equation ^ = y. Whence, the inertia due 
“ to B alone, or 
(t)‘ 
“ will be the correct measure of the adhesive air dragged by that body alone." 
We thus obtain a method of exhibiting separately the effect of the air on a 
sphere, cylinder, or other body (B) fastened to a rod (A) at any distance from 
the point of suspension. In the subsequent Tables therefore, I have annexed 
another collateral column, indicating in each case the effect of the air, or the 
increase of inertia, due to the suspended body alone, (without regard to the 
rod,) deduced agreeably to the above formula. I shall now proceed to the de¬ 
tail of the experiments ; commencing with those which determine the effect 
due to the rods alone. 
It will be seen that, amongst the preceding experiments, there are some 
made on a long brass cylindrical tube (No. 35—38), and on a long copper 
cylindrical rod (No. 21) : and that the former, which is 1^ inch in diameter, 
