132

PTOLEMY versus COPEKNKJUS.

also be observed that in the figure a motion of rotation fromwest to east round the Sun is supposed to take place in adirection the reverse of that in which the hands of a watch,whose face would be represented by one of the circles, wouldrevolve. This direction of motion is indicated by all thearrows, except those in the highest row, which are drawnto represent motion from east to west.

We hope that a little meditation upon the diagram in Fig . XL.may enable our readers to see that Venus, according to the

E E,

Fig. XL.—Showing how the motions of Venus and of the Earth in their orbits causethe progression and retrogression of Venus in its apparent path.

Copernican theory, would appear to move onwards, or fromwest to east, amongst the stars, from the position Vi to aboutthe position v 3 , and, again, from somewhere near to v e on to v-;and that it would always appear so to move except betweensuch a position as v,, and such an one as v e , during which timeit would appear to travel from v 3 to v 4} and then past v s on tov e , in the reverse direction. This temporary reversal of itsmovement, or its retrogression, is therefore very simply ac-counted for, as a result of the theory in cprestion, by the way in