DENSITY OF THE EARTH. 31 



Cavendish, with exceedingly delicate apparatus, observed 

 the attraction of masses of known weight and size upon 

 each other. Applying the powers of arithmetical cal- 

 culation, and the data obtained from the small experi- 

 ments to the larger phenomena, Maskelyne determined 

 the earth's mean density to be 4*71, whilst Cavendish 

 made it 5*48, but the more recent refined investigations 

 of Baily have determined it to be 5*67.* 



From data thus obtained by severe inductive experi- 

 ments and mathematical analyses, the astronomer, by 

 observing the deviations of a distant star, is enabled to 

 determine the influence of those stellar bodies near 

 which it passes, and, hence, to calculate the relative 

 magnitudes of each. The accuracy of the law is in this 

 way put to the severest test, and the precision of astro- 

 nomical prediction is the strongest proof of its univer- 

 sality and truth. 



Rolling onward its lonely way, in the far immensity 

 of our system, the planet Uranus was discovered by 

 the elder Herschel, so great its distance that its 

 diminished light could scarcely be detected by the 

 most powerful telescopes; but since its discovery its 

 path has been carefully watched, and some irregularities 

 noticed. Most of these disturbances were referable 

 to known causes ; but a little alteration in its rate of 

 motion observed when the planet was in one portion 

 of its vast orbit ,was unexplained. Convinced of the 

 certainty of Newton's law, and having determined 

 that the attraction of known masses was insufficient 



perintendence of it to the eiid of his life, from its first publication 

 in 17G7, are mentioned in the Almanack (vol. i. p. 3C4) ; his Sche- 

 hallion Experiment on Attraction in vol. iii. p. GO ; and the charac- 

 ter of his Greenwich Observations in Greenwich Observatory in vol. 

 ii. p. 442. 



* Experiments to determine the Density of the Earth. By Henry 

 Cavendish, Esq., F.ll.S. and F.A.S. Philosophical Transactions, 

 1798. 



