eee a ge RE Pace eee, hg cd ae fy a eee cate 
Been wae ee ae Se age c = 
J. Lovering on Velocity of Light and the Sun’s Distance. 171 
similar reflexion 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. Lubboch, by combining Airy’s empirical determination 
of the coéflicient with the mass of the moon as he finds it from © 
the tides (viz: ;,), makes the solar parallax 8-84. If the mass 
of ,; 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 Theory 
of the apparent motion of the Sun, deduces a solar parallax of 
895 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 Method. Parallax. Distance. 
Computer : 
Encke, By Venus (1761), 37-53 95141830 miles} 
Encke, “  # (2769), 3 59 95820610 
ille, By Mars, 10’”-20 76927900 
enderson, oa ) -03 90164110 
Gilliss and Gould, CaP oe ‘50% 961 
—— _— SN al 
Mayer, By Moon, 7/"-80 ~ 104079100 
Burg, “ 8 “62 
Laplace, “« « 8 61 915 
Pontecoulant, «  « 8 63 94689710 
Lubboch, “ « 3 84 92313580 
. « « 8 81 92652970 
n,  * 8 -88 91861060 
Leverrier, “« « 8 95 91066350 
Foucaul light, 8’"86 92087342 
Sage - “ 8 51 95117000 
Velocity of light, By eclipses 193350 
* « « aberration, 191513 
“ « « Fizeau’s experiment, 194667 
= * « Foucault’s experiment, 185177 
Foucault’s experiment on the velocity of light has been 
Popularly announced as ing a “revolution in astronomical 
Science.” But it appears from the preceding sketch that it has 
Taised no new question in astronomy, though it may have at- 
