534 



Prof. Lovering on "the Velocity of Light 



tenelle had said that Newton, without getting out "of his arm- 

 chair, found the figure of the earth more accurately than others 

 had done by going to the ends of the earth. Laplace makes a 

 similar reflection on this new triumph of theory, " It is won- 

 derful that an astronomer, without going out of his observatory, 

 should be able to determine exactly the size and figure of the 

 earth, and its distance from the sun and moon, simply by com- 

 paring his observations with analysis, the knowledge of which 

 formerly demanded long and laborious voyages into both hemi- 

 spheres." The accordance of the results obtained by the two 

 methods is one of the most striking proofs of universal gravita- 

 tion. Pontecoulant makes the solar parallax by this method 

 8"* 63. Lubbock, by combining Airy's empirical determination 

 of the coefficient with the mass of the moon as he finds it from 

 the tides (viz. -^f), makes the solar parallax 8' ;, 84. If the mass 

 of Tf$ is substituted, the parallax is changed to 8"*81. Finally, 

 Hansen, in his new ' Tables of the Moon/ adopts 8"-8762 as-the 

 value of the solar parallax. Moreover, Leverrier, in his f Theory 

 of the Apparent Motion of the Sun/ deduces a solar parallax of 

 8 ,/# 95 from the phenomena of precession and nutation. 



The conclusions of this whole review are summed up in the 

 following Table, in which the values of the solar parallax and 

 of the sun's distance, by the three methods of astronomy, and 

 by the experiment of Foucault, are placed in juxtaposition ; also 

 the different velocities of light found by astronomical observa- 

 tions and by experiment. 



Observer or computer. 



Method. 



Parallax. 



Distances. 



Encke 



ByVenus(1761)... 

 „ (1769)... 



8-53 

 8-59 



miles. 

 95141830 

 95820610 



Encke 





Lacaille 



By Mars 



10-20 

 903 

 8-50 



76927900 

 90164110 

 96160000 



Henderson 



>> 



Gilliss and Gould.. 





By Moon 



7-80 

 8-62 

 8-61 

 8-63 

 8-84 

 8-81 

 8-88 

 8-95 



104079100 

 94802440 

 94915970 

 94689710 

 92313580 

 92652970 

 91861060 

 91066350 











Pontecoulant 



" 



" 

















" 





By light 



8-86 

 8-51 



92087342 

 95117000 











Velocity of light... 

 »» »» 





193350 

 191513 

 194667 

 185177 





By Fizeau's experii 

 By Foucault's expe 









