ASTRONOMY. 19 



the deductions obtained from the pendulum and 

 actual measures of arcs, when used to confirm each 

 other, is rather remarkable. The French commission 

 inferred an ellipticity from measurement of -g-^; 

 Laplace calculated the compression from fifteen 

 lengths of the pendulum at -j-J-g, but a logarithmic 

 error was subsequently discovered, which increased 

 it to -3-^. Since then the compression deduced from 

 the measurement of more distant arcs became ^-g ; 

 and that from the inequalities of the lunar motion 

 3-^, the same author inferred an ellipticity from the 

 pendulum of ^^, showing a most extraordinary and 

 variable facility of agreement. 



The ellipticity (j^$) given as the result of recent 

 experiments, differs more considerably than could 

 have been expected from -3-^-, which had previously 

 been received on the authority of the most eminent 

 mathematician of the age (Laplace) as the concurrent 

 indication of the measurement of terrestrial degrees, 

 of pendulum experiments, and of the lunar irregula- 

 rities dependant on the oblateness of the earth. This 

 variation in the results is occasioned by the deflection 

 that the plumb-line undergoes, owing to the unequal 

 density of the materials near the surface of the earth, 

 and which affects the celestial determination of the 

 latitudes at the extremity of the measured arcs. 



Star in the Zenith. 



No star has been yet observed absolutely in the 

 zenith. This might be done under the equator, 

 where an instrument fixed on granite, or aperture 

 bored through a solid stratum, would reduce the pro- 

 blem to the simplest of all conditions. 



c2 



