390 W. Harkness—The Solar Parallax. 
earth and the sun, and combining this with the measured veloc- 
ity of light, we have 
tanp = no | (26) 
2d. Assuming the ratio of the earth’s orbital velocity = 
the velocity of light to be represented by the constant of a 
ration, and combining that constant with the measured valboity 
of light, we have 
om 27 
tan? = PV tan aie es 
If p and V are eliminated between (26) and (27) we get 
2 70 
tan a = 28 
Pie (28) 
which shows the relation between @ and @. 
or the constants in these equations I adopt 
p =6378°39 kilometers (Col. Clarke’s value). 
T=31,558,149 seconds of mean time. 
é,=0°016771 
and the equations become 
_ [9711914] (29) 
Vv 
__ [773269] 6 
6 = [138644 ]a (31) 
the apna within the square brackets being the logarithms 
of the ers which they represent. In connection with 
biidations (26), (27), 28) the reader may sahaalt Cornu, OPM, 
xiii, pp. A 299-A 301. 
Velocity of Light.—The following are the principal experi- 
mental determinations of the velocity of light between points 
upon the earth’s surface : 
Kilometers. 
1649. Fiean (CRA, 1849, t. xxix, p. 90), ..-... .--.-.-- 315,320 
1862. Foupaule (CRH, 1862, t. lv, p. 796: Recueil des 
vaux scientifiques de e Léon Foucault, pp.216 a8), 298,000 
Tee. Coreg (Ore, £1, 208), se ne concen 300,40 
1876. Helmert (ANn, 1876, Dd. Texxyu, & 196),...-.-.-- 299,090 
1879. Michelson (Proc. Amer. Assoc., tery) pp- 124-160), 299,940 
1881. Young and Forbes (Nature, 1881, vol. XXiv, p. 303), 301,382 
Light Equation—The time taken by light to traverse the 
mean radius of the earth’s orbit is commonly called the light 
si and there are but two determinations of it from the 
eclipses of Jupiter’s satellites, namely :* 
