10;?
Fig . XXJV., in which the apparent annual path of the Sun isalso shown. We mean that Mercury and Venus are alwaysobserved in close apparent proximity to the Sun, while all theother planets may be seen at any distance from it, and even inthe very opposite part of the Zodiac, or belt of the heatens inwhich their paths lie, to that in which the Sun is found at anygiven time.
Let us therefore consider a little more particularly the variousobservations of the planets which it was possible to make'before the invention of the telescope, so that we may the better
Fig. XXVIII.—Apparent path of Mars, as seen from the Earth , m 1&77, ls78, and 1870.
understand what the ancients knew, and appreciate the skillwith which the theory of the movements of the Solar System ,which was invented and elaborated by Hipparchus, Ptolemy ,and their successors, was contrived to explain what seemed tobe so complicated.
To beg in with the planet Mercury , it must be rememberedthat it was never very easy to see it, even when it was mostfavourably situated, owing to the strong glare of the morningor evening twilight. The first important step towards thedetermination of the true nature of its orbit was the discovery