Memoir of the late Francis Bally, Esq.^ F.R.S.^ 8^c. 61 



ill-understood disturbing causes, set themselves in opposing 

 array in their most recondite and unexpected forms of inter- 

 ference. Nor could it have been overlooked by him that it 

 was necessary, not merely to do over again what Cavendish 

 had done before him, a thing in itself not easy, but to do it 

 much more thoroughly and effectually. 



Mr. Daily, however, was not to be discouraged by such 

 considerations. He saw that there existed a blank in our list 

 of exact data which it was necessary to fill, and he felt himself 

 in possession of those gifts of nature and position which en- 

 abled him to fill it. Accordingly in 1835, on the occasion 

 above alluded to, the Astronomical Society appointed a com- 

 mittee to consider the subject ; and Mr. Bally having offered 

 to perform the experiment, in 1837, the Government (at the 

 instance of Mr. Airy) granted the liberal sum of 500/. to defray 

 the cost of the experiment. 



This great work was brought to a satisfactory conclusion in 

 184-2, and a complete account, with a full detail of the expe- 

 riments, printed in one volume, published in 1843, forming 

 the fourteenth of the series of Transactions of this Society. 

 The experiments were varied with balls of different materials, 

 and with suspensions no less various, combined so as to form 

 no less than 62 distinct series, embodying the results of 2153 

 experiments; and which, formed into groups according to the 

 nature of the combination, afford 36 distinct results, taking 

 those only in which the balls were used, the extremes of which 

 are 5*847 and 5*507, and the most probable mean 5*660, none 

 of them being so low as Cavendish's mean result, 5'44'8. The 

 probable error of the whole (00032) shows that the mean 

 specific gravity of this our planet is, in all human probability, 

 quite as well determined as that of an ordinary hand-specimen 

 in a mineralogical cabinet, — a marvellous result, which should 

 teach us to despair of nothing which lies within the compass 

 of number, weight and measure. I ought not to omit men- 

 tioning that, of all the five determinations of this element we 

 possess, Mr. Baily's is the highest*. 



Though it would be equally remote from my present pur- 

 pose, and superfluous in presence of such an assembly, to enter 



* The five determinations alluded to are, in order of magnitude, as fol- 

 lows: — 

 Schehallien experiment from Playfair's data 1 Max... 4"867\ «» A'7^'^ 



and calculations J Min...4-559 / ' 



Carlini, from pendulum on Mont Cenis, corrected byGinlio 4"950 



Reich, repetition ofCavendish'sexpt. (most probable combination) ... 5-438 



Cavendish, computation corrected by Baily 5*448 



Baily (most probable combination) 5"660 



