118 Mr. Baily's Experiments with the Torsion-rod 



that the results soon convinced him that the proper mode had 

 been taken for the removal of the principal source of discord- 

 ance. For although, in some cases, slight discrepancies may 

 still appear to exist, as might be expected in any inquiry that 

 involves so delicate a system of operations, yet where the dis- 

 cordances are of greater magnitude they seem to be confined 

 to one class of experiments, and to depend principally on the 

 nature and construction of the material of which the suspen- 

 sion-line or torsion-rod is composed, and do not materially 

 affect the general result of the whole. In fact, Mr. Baily states 

 that he has since met with very few experiments, made in the 

 regular mode of proceeding, that are objectionable, or that 

 need be rejected. Every experiment therefore that has been 

 made, under this new arrangement of the apparatus (whether 

 good, bad, or indifferent), has been recorded and preserved; 

 and they are all given without any reserve whatever ; it being 

 left to the reader himself to reject or retain, at his pleasure, 

 such as he may think fit. 



After these introductory remarks, the author proceeds to 

 the several modes of carrying on the regular system of opera- 

 tions which he had undertaken. With respect to the torsion- 

 rod, he states that it is never at absolute rest, but is constantly 

 in a state of vibration on its centre ; and consequently when 

 the end of it is viewed at a distance with the telescope, it ap- 

 pears to oscillate on each side of a mean point, called the 

 resting-point. For, even when it is apparently in a state of 

 complete repose, minute vibrations are always perceptible with 

 the telescope ; and the times of performing such infinitesimal 

 arcs correspond, in most cases, very nearly with the mean 

 time of vibration that takes place when the torsion-rod is in 

 full action. Mr. Baily however observes, that this resting-point 

 is by no means permanent or stationary, and seldom remains 

 in the same position for any length of time, even when the 

 torsion-rod is not influenced by the approach of the masses. 

 The extent and direction of its disturbance, as well as its rate 

 of motion when so disturbed, are very variable, and seem to 

 depend on causes which have not been sufficiently accounted 

 for, but which may in some measure arise either from slight 

 changes of temperature, or some latent alteration in the com- 

 ponent parts of the suspension-line. These vibratory motions 

 of the resting-point (which must be carefully distinguished 

 from the regular vibratory changes in the position of the 

 torsion-rod itself, caused by the near approach of the masses) 

 do not materially affect the mean results in a series of experi- 

 ments ; more especially if their march be regular. It is only 

 when any sudden and considerable transition takes place, that 



