OF FLUIDS ON THE MOTION OF PENDULUMS. 



[71] 



sure and temperature was the l-770th of that of water, so that in the calculations from theory 

 it is to be supposed that a-' 1 = 770. 



If w be the weight of the whole pendulum, w that of the air which we must suppose 

 attached to the pendulum at its centre of gyration in order to express the effect of the inertia 

 of the air, S the vibrating specific gravity of the pendulum, the effects of buoyancy and inertia 

 are as aS' 1 to w'w~ l ; but they are also as 1 to It-1, according to the definition of the fac- 

 tor n, and therefore 



w 



(tt-l)^w, 



(155) 



a formula which may be employed to calculate w when tl is known. 



Baily's results with spheres at the ends of long rods. 



With respect to the two experiments marked ? Baily remarks, " These two experiments 

 (with the pendulums Nos. 50 and 51) are very unsatisfactory ; and are marked as such in my 

 journal. It was consequently my intention to have repeated them : but the subject was over- 

 looked till it was too late. I should propose their being rejected altogether." If these two 

 experiments be struck out, it will be seen that the differences between theory and experiment 

 are very small, especially when the difficulty of this set of experiments is considered, arising 

 from the frequency of the coincidences with the mean solar clock. 



59. On account of the difficulty which Baily experienced in obtaining accurate results 

 with the long rods and spheres attached, he divided the brass and steel rods near the centre 

 of oscillation, and after having cut off an inch from each portion inserted the spheres where 

 the rods had been divided. The results thus obtained constitute the 15th set of experiments. 

 He afterwards removed the lower segments of the rods, and obtained the results contained in 

 the 16th set. I shall give the computation of the latter set first, inasmuch as the formulae to 

 be employed are exactly the same as those required for the 14th set. The experiments belong- 

 ing to this set in which the spheres were swung with iron wires have already been computed 

 under the head of spheres attached to fine wires. 



