62 D. P. Todd—Solar Parallax from the Velocity of Light. 
The next step is the combination of this value with astro- 
nomical constants, for the determination of the distance of the 
center of the sun from the center of the earth. 
eory and observation of the satellites of Jupiter afford 
a determination of the time-interval required by light in 
traversing the mean radius of the orbit of the earth. Only two 
first satellite of Jupiter from 1848 to 1873. The results of the 
two determinations are as follow :— 
elambre, 493°-2; Glasenapp, 500°°84 + 15-02. 
It is quite impossible to judge with certainty just how a 
two widely discordant values should be combined. The form 
determination rests on a much greater number of obsepaaal 
than the latter; but it is difficult to form a just estimate of the 
worth of an average last-century observation ne an eclipse eo a 
satellite of J upiter. And, moreover, astronomers have n 
means of knowing the process of i te ehek led ce 
distinguished French astronomer to his result—which he has 
adopted in his own tables of the satellites, and which was 
adop y Damoiseau in his Tables liptiques, published in 
836. The latter determination rests upon a mass of observa- 
tions of definite excellence, which have been discussed after 
the modern fashion. I combine the two values giving weight 
unity to the first, and weight two the second. The “adopted 
alue of & is, therefore, 498°, which, combined with the con- 
stant of light- -velocity — deduced gives the mean radius of 
the orbit of the earth equal to 
149,450,000 kilometers= 92,866,000 miles. 
If, now, we combine this result with the value of the equa- 
torial radius of the earth derived by Listing,t 
a = 6877377 3 tered 
= 3962™°790 | 3°5980011 
there results the mean equatorial horizontal parallax of the — 
sun, 8802. 
(IL) The velocity of light, the constant of aberration, and 
appropriate elements of the terrestrial orbit are combined, the 
equation of connection being, 
* Tables Ecliptiques des Satellites de Jupiter, par Delambre, Paris, 1819. 
t Cpasnenie Hasswgeniii 3arwbaili Cayrsuxoss JOuntepa Cp Tasangaun Sarmbuili 8 
Mem ay Cosow ... . Taasenana . . C.—Hetepsypre. | os. 1OIe 
Erdkérpers. ine Fortset- 
zung der | cerammerssny iiber unsere jetzige Kenntniss der Gestalt und Grosse 
der Erde. Von Johann Benedict Listing. Gdéttingen, 1878. 
