60 Memoir of the late Francis Baily, Esq.y F.R.S., 5fc. 



satisfactory, otherwise than as a first step towards more pre- 

 cise determinations. Mr. Daily's labours, therefore, on the 

 pendulum were hardly brought to a conclusion when he was 

 led to enter upon this subject, the immediate occasion of his 

 doing so being an incidental suggestion at the council-table by 

 Mr. De Morgan, of the desirableness of repeating the expe- 

 riment of Cavendish* — a suggestion immediately seconded 

 both by the Astronomer Royal and by Mr. Baily. The ex- 

 perience of the latter had shown him how indispensably ne- 

 cessary, in such incjuiries, are extensive repetition and variation 

 of circumstance. The Schehallien experiment, from its very 

 nature, admitted of neither; and, on carefully examining Ca- 

 vendisli's record of his own experiment, he found abundant 

 reason to perceive how much was left to be desired, in both 

 these respects, even in that form of the inquiry. 



In resolving on a repetition of this experiment, the difficulty 

 of the undertaking itself, and his own preparation for it, must 

 have been, and no doubt were, very seriously considered. 

 However confident in his own resources and perseverance, it 

 was no holiday task in which he was now about to engage. 

 The pendulum experiments, with all their delicacy, could 

 hardly be regarded as more than an elementar}' initiation into 

 the extreme minuteness necessary for this inquiry. There are 

 two branches of research in physical astronomy which task to 

 the utmost the resources of art, the delicacy of manipula- 

 tion, and the perseverance of the inquirer — the parallax of the 

 fixed stars, and the density of the earth. In both, an immense 

 object has to be grasped by the smallest conceivable handle. 

 But of the two problems, the latter is probably that which 

 throws the greatest burden on the inquirer, inasmuch as it is 

 not merely a series of observations to be carried on under 

 well-ascertained circumstances and known laws, but a course 

 of experiments to be entered on for eliminating or controlling 

 influences which war against success in every part of the pro- 

 cess, and where every element, nay, even the elementary 

 powers of heat, electricity, magnetism, the molecular move- 

 ments of the air, the varying elasticity of fibres, and a host of 



* Fiat justitia, ruat caelum. The original design of this beautiful expe- 

 riment was Mitchell's, who actually constructed the identical apparatus 

 which Cavendish used, but died before he could execute the experiment. 

 The apparatus came, after his death, into the possession of the Rev. W. H. 

 Wollaston, D.D., who gave it to Cavendish, who used it, indeed, to excel- 

 lent purpose, but who assuredly neither devised the experiment, nor in- 

 vented, nor constructed, nor even, so far as I can perceive, materially im- 

 proved the apparatus. All this is distinctly stated by Cavendish himself, 

 who is, therefore, no way to blame for any misconception which may pre- 

 vail on the subject. 



