92     ON THE EFFECT OF THE INTERNAL  FRICTION  OF  FLUIDS
of experiments the spheres did not materially affect the time of vibration, inasmuch as they were inserted nearly at the centre of oscillation of the rods, and therefore in this case the process is legitimate. Accordingly, I think it is a sufficient comparison between theory and experiment in the case of the 15th set, to compare the weights of air due to the spheres alone, as calculated by Baily, with the weights calculated according to the theory of this paper with the assumed value of vV- I have exhibited separately the weight corresponding to the correction for confined space, in order to enable the reader to form an estimate of the extent to which the results may be affected by the uncertainty relating to the amount of this correction.
Weights of air dragged by the spheres alone, as deduced from Baily's results with the spheres at the centre of oscillation of the long rods.
By Theory
	ij-inch sphere	2-inch sphere	3-inch sphere	
In free air Additional for confined space	0-431 0-006	1-060 0-048	3-002 0-476	
Total	0-437	1-108	3-478	
Difference, theory and experiment, as decimal	-0-012	+0-001	-o-ioi	
By Experiment
	li-inch sphere	2- inch sphere	3-inch sphere	
From experiments with brass rod From experiments with steel rod	0*446 0-405	1-180 1-039	3-382 3-371	
Mean	0-425	1-109	3-377	
Difference, as fraction of the whole	i
:'i«Y	+ TlVs	-A	
62. I pass now to Bessel's experiments described in his memoir entitled Untersuchungen uber die Lange des ewfachen Sekundenpendels, which is printed among the memoirs of the Academy of-Sciences of Berlin for the jear 1826. The object of