At the beginning as at the end of my voyage,, 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), traveller 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 away from it, but hardly able to overtake a planet that should lie far out of my line of advance or retreat, while moving at full speed away from me. In order to secure a chance of retreat, it was desirable as long as possible to keep the Earth between the Astronaut and the Sun; while steering for that point in space where Mars would lie at the moment when, as seen from the centre of the Earth, he would be most nearly opposite the Sun,—would cross the meridian at midnight. It was by these considerations that the course I henceforward steered was determined. By a very simple calculation, based on the familiar principle of the parallelogram of forces, I gave to the apergic current a force and direction equivalent to a daily motion of about 750,000 miles in the orbital, and rather more than a million in the radial line. I need hardly observe that it would not be to the apergic current alone, but to a combination of that current with the orbital impulse received at first from the Earth, that my progress and course would be due. The latter was the stronger influence; the former only was under my control, but it would suffice to determine, as I might from time to time desire, the resultant of the combination. The only obvious risk of failure lay in the chance that, my calculations failing or being upset, I might reach the desired point too soon or too late. In either case, I should be dangerously far from Mars, beyond his orbit or within it, at the time when I should come into a line with him and the Sun; or, again, putting the same mischance in another form, behind him or before him when I attained his orbit. But I trusted to daily observation of his position, and verification of my "dead reckoning" thereby, to find out any such danger in time to avert it.

The displacement of the Earth on the Sun's face proved it to be necessary that the apergic current should be directed against the latter in order to govern my course as I desired, and to recover the ground I had lost in respect to the orbital motion. I hoped for a moment that this change in the action of the force would settle a problem we had never been able to determine. Our experiments proved that apergy acts in a straight line when once collected in and directed along a conductor, and does not radiate, like other forces, from a centre in all directions. It is of course this radiation— diffusing the effect of light, heat, or gravity over the surface of a sphere, which surface is proportionate to the square of the radius—that causes these forces to operate with an energy inversely proportionate, not to the distance, but to its square. We had no reason to think that apergy, exempt as it is from this law, would be at all diminished by distance; and this view the rate of acceleration as I rose from the Earth had confirmed, and my entire experience has satisfied me that it is correct. None of our experiments, however, had indicated, or could well indicate, at what rate this force can travel through space; nor had I yet obtained any light upon this point. From the very first the current had been continuous, the only interruption taking place when I was not five hundred miles from the Earth's surface. Over so small a distance as that, the force would move so instantaneously that no trace of the interruption would be perceptible in the motion of the Astronaut. Even now the total interruption of the action of apergy for a considerable time would not affect the rate at which I was already moving. It was possible, however, that if the current had been hitherto wholly intercepted by the Earth, it might take so long a time in reaching the Sun that the interval between the movement of the helm and the response of the Astronaut's course thereto might afford some indication of the time occupied by the current in traversing the 96-1/2 millions of miles which parted me from the Sun. My hope, however, was wholly disappointed. I could neither be sure that the action was instantaneous, nor that it was otherwise.