352

THE SATELLITES OF JUPITER .

through the points m 9 , m 8 , m 7 , etc., indicates the actual pathof the Satellite in space, which is evidently of the form shownin the diagram.*

Fig . LXXXI. is drawn in a similar manner for the 1stSatellite, only upon a much larger scale, so that j^, which isthe distance travelled by Jupiter in about 42£ hour's, onlyrepresents about 1,240,000 miles ; while the distance fromJupiter to this Satellite is about 262,000 miles; i.e., about£§, or not quite 4th of j 9 j 7 . With this exception the methodby which the actual path of the Satellite is obtained is thesame as in Fig. LXXX. It is evident, as would also follow

Fig . LXXXI.—The actual path of the 1st Satellite of Jupiter in space duringone of its months.

from our previous statement as to the retrograde motion of theSatellite when in the position of new moon (as at m 5 ), that theorbit in space is looped as is shown in the figure.

We have already exceeded the limits to which we intendedto restrict our discussion of these four Moons. Our excusemust be, that iu them and the planet round which they circlewe have what we might almost be justified in calling a minia-ture Solar System . We have seen in our last lecture, that, the

* It would have been better both in Figs. LXXX. and LXXXI. ifthe letters had been numbered from right to left, instead of from left toright, as the former direction is that in which in our previous figures we havetaken Jupiter to move. The Sun is supposed to be situated beneath eachdiagram.