for determining the Mean Density of the "Earth. 113 



inquiry, notwithstanding this apparent confirmation of Caven- 

 dish's results. Various places were suggested, by different 

 persons, as the most suitable and fit for performing experi- 

 ments of this kind : but, after inspecting several situations that 

 were proposed, and considering all the circumstances of the 

 case, Mr. Baily at length decided to carry them on at his own 

 house, which he considers to be not only the most convenient 

 that he could have selected, but which he has since found to 

 be as suitable and fit as any that could have been specially 

 erected for the express purpose. This house stands detached 

 from any other building, in a large garden, some distance 

 from the street, and consists of one story only. 



The author then proceeds to give a description of the room 

 in which the experiments were made, and likewise of the ap- 

 paratus that was constructed for this special purpose. Al- 

 though the apparatus was in a general view similar to that 

 of Cavendish, yet in some respects it was essentially different. 

 The great balls (or masses, as they are called) were suspended 

 from the ceiling by Cavendish and Reich: but Mr. Baily sup- 

 ported them, from the floor, on a plank which turned on a pivot, 

 and suspended the small balls from the ceiling ; thus reversing 

 the mode of operations. This method of moving the masses 

 he considers to be a great improvement : for he says, " Nothing 

 can exceed the ease, the steadiness, and the facility with which 

 these large bodies are moved : and during the many thousands 

 of times that they have been turned backwards and forwards, 

 I have never observed the least deviation from the most per- 

 fect accuracy. At the final close of all the experiments, the 

 pivot turns as steadily, as freely, and as accurately as at the 

 commencement of the operations." The small balls were also, 

 by Cavendish and Reich, suspended by a fine wire from the 

 ends of the torsion-rod ; whereas Mr. Baily screwed them to 

 the ends of the torsion-rod, of which they thus formed an in- 

 tegral and solid portion. The motion of the torsion-rod was 

 observed by means of a reflected image of the scale, from a 

 small mirror attached to the centre of the torsion-rod, in the 

 manner proposed by Gauss in magnetical experiments*, and 

 adopted by Reich. Some other alterations were likewise made 

 in the construction and arrangement of the apparatus, to 

 which it is unnecessary to allude more minutely on the pre- 

 sent occasion. 



Mr. Baily made use occasionally of several small balls, of 

 different sizes, and formed of different substances, with a view 



[* See Phil. Mag. Third Series, vol. ii. p. 296 : also Taylor's Scientific 

 Memoirs, vol. ii. p. 31, — Edit.] 

 Phil Mag. S. 3. Vol. 2 1 . No. 1 36. Aug. 1 842. I 



