DETERMINATION OF THE SOLAR PARALLAX. 335 
Laplace has solved the problem numerically without a 
base of any kind whatever; he has deduced the distance 
of the sun from observations of the moon made in one 
and the same place ! 
The sun is, with respect to our satellite, the cause of 
perturbations which evidently depend on the distance of 
the immense luminous globe from the earth. Who does 
not see that these perturbations would diminish if the 
distance increased ; that they would increase on the con- 
trary, if the distance diminished ; that the distance finally 
determines the magnitude of the perturbations ? 
Observation assigns the numerical value of these per- 
turbations ; theory, on the other hand, unfolds the general 
mathematical relation which connects them with the solar 
parallax, and with other known elements. The determi- 
nation of the mean radius of the terrestrial orbit then 
becomes one of the most simple operations of algebra. 
Such is the happy combination by the aid of which 
Laplace has solved the great, the celebrated problem of 
parallax. It is thus that the illustrious geometer found 
for the mean distance of the sun from the earth, ex- 
pressed in radii of the terrestrial orbit, a value differing 
only in a slight degree from that which was the fruit of 
so many troublesome and expensive voyages. According 
to the opinion of very competent judges the result of the 
indirect method might not impossibly merit the prefer- 
ence.* 
* Mayer, from the principles of gravitation ( Theoria Lune, 1767), 
computed the value of the solar parallax to be 7//*8. He remarked 
that the error of this determination did not amount to one twentieth 
of the whole, whence it followed that the true value of the parallax 
could not exceed 8//-2. Laplace, by an analogous process, determined 
the parallax to be 8/45. Encke, by a profound discussion of the 
observations of the transits of Venus in 1761 and 1769, found the 
value of the same element to be 8/!-5776.— Translator. 
