At the beginning as at the end of my voyage, I steered a distinct course, governed by considerations quite different from those which controlled the main direction of my voyage. Thus far I had simply risen straight from the Earth in a direction somewhat to the southward, but on the whole "in opposition," or right away from the Sun. So, at the conclusion of my journey, I should have to devote some days to a gradual descent upon Mars, exactly reversing the process of my ascent from the Earth. But between these two periods I had comparatively little to do with either planet, my course being governed by the Sun, and its direction and rate being uniform. I wished to reach Mars at the moment of opposition, and during the whole of the journey to keep the Earth between myself and the Sun, for a reason which may not at first be obvious. The moment of opposition is not necessarily that at which Mars is nearest to the Earth, but is sufficiently so for practical calculation. At that moment, according to the received measurement of planetary distances, the two would be more than 40 millions of miles apart. In the meantime the Earth, travelling on an interior or smaller orbit, and also at a greater absolute speed, was gaining on Mars. The Astronaut, moving at the Earth's rate under an impulse derived from the Earth's revolution round the Sun (that due to her rotation on her own axis having been got rid of, as aforesaid), travelled in an orbit constantly widening, so that, while gaining on Mars, I gained on him less than did the Earth, and was falling behind her. Had I used the apergy only to drive me directly outward from the Sun, I should move under the impulse derived from the Earth about 1,600,000 miles a day, or 72 millions of miles in forty-five days, in the direction common to the two planets. The effect of the constantly widening orbit would be much as if the whole motion took place on one midway between those of the Earth and Mars, say 120 millions of miles from the Sun. The arc described on this orbit would be equivalent to 86 millions of miles on that of Mars. The entire arc of his orbit between the point opposite to that occupied by the Earth when I started and the point of opposition—the entire distance I had to gain as measured along his path—was about 116 millions of miles; so that, trusting to the terrestrial impulse alone, I should be some 30 millions behindhand at the critical moment. The apergic force must make up for this loss of ground, while driving me in a direction, so to speak, at right angles with that of the orbit, or along its radius, straight outward from the Sun, forty odd millions of miles in the same time. If I succeeded in this, I should reach the orbit of Mars at the point and at the moment of opposition, and should attain Mars himself. But in this I might fail, and I should then find myself under the sole influence of the Sun's attraction; able indeed to resist it, able gradually to steer in any direction