564 Royal ImtittUion. •,.,«.,'' 



tude described by tKe centre and extremity of the meridional dia- 

 meter of the table." (See Mechanics' Mag., May 3 and 10, 1851.) 

 The lucid and able illustrations of the subject given by Professor 

 Sylvester have thrown much light on the explanation. 



Modifications of the principle have been suggested by M. Chasles, 

 on the idea of the difference of rotatory velocity between any two 

 points on the same meridian ; which difference, insensible as it might 

 seem to be for the minute length of a vibration, he shows will in 

 successive vibrations become sensible. This idea is nearly the same; 

 as that announced by Laplace (^Mecaniqne Celeste, vol. iv. c. 5), who 

 infers a deviation in the plane of a projectile fired in the direction of 

 the meridian. The same idea has been discussed also by other 

 mathematicians, and has been further carried out by M. Poinsot, 

 who has suggested, that if two balls suspended by separate strings, 

 hanging together in contact, and consequently both partaking in the' 

 velocity of rotation of that point of the earth, were to be suddenly 

 separated by releasing a spring placed between them, and at first 

 confined by a string, they would then show the difference of velocity 

 belonging to points on the earth at that distance apart, and would 

 consequently revolve round the vertical. (See Comptes JRendus^ 

 1851, No. 14.) 



A beautiful variation of the experiment has been suggested by 

 M.^ray diis^Comptes Rendus, l851,No.6),in which a. perfectly c\rcM\aix 

 motion is communicated to a pendulum (by a peculiarly ingenious 

 contrivance), the time of whose revolution will be diflTerent according 

 as its direction conspires with or opposes that of the earth. -. 



If all torsion in the thread could be got rid of, a ball simply sus-, 

 pended and furnished with an index in its equator would be seen to 

 rotate. But the torsion destroys the effect. This is the suggestion 

 of M. Baudrimont {Comptes Rendus, 1851, No. 8). 



But by far the most complete idea, not only of the general prin- 

 ciple, but of the precise law of the sine of the latitude, is obtained 

 from the beautiful apparatus constructed by Mr. Wheatstone, in ' 

 which the pendulum is replaced by the vibrations of a coiled spring, 

 the axis of which can be placed in any required inclination or lati- 

 tude with respect to a vertical semicircular frame, which is made to 

 revolve about its vertical radius, and the direction of the vibrations 

 is seen to change in a degree proportioned to the sine of the latitude 

 or inclination, as for example, for lat. 30 the sine —\; and conse- 

 quently if the vibration be originally in the meridian, when the 

 meridian has revolved 180", the deviation =180°xi=90°, or is at 

 right angles to the meridian. 



Thisapparatuswasexhibitedatthelecture,andis described at p.572. 

 Upon the whole, the experiment is one of high interest and import- 

 ance; some discrepancies or difficulties in the different views taken 

 of the theory as well as in the observed results, seem to indicate 

 that the subject, however apparently simple, has not yet been tho- 

 roughly worked out, and to point to the desirableness of further 

 repetitions of the experiments, if possible in vacuo, and with increased 

 precautions, as well as to a revision of the dynamical and analytical 

 processes, by which possibly any seeming difficulties may be cleared up. 



