as from the external edge of the mirror, was exactly equal to the Sun’s circumference when presenting the largest disc he ever shows to an observer on Earth.  Each inner circle corresponded to a diameter reduced by one second.  By means of a vernier or eye-piece, the diameter of the Sun could be read off the discometer, and from his diameter my distance could be accurately calculated.  On the further side of the machinery was a chamber for the decomposition of the carbonic acid, through which the air was driven by a fan.  This fan itself was worked by a horizontal wheel with two projecting squares of antapergic metal, against each of which, as it reached a certain point, a very small stream of repulsive force was directed from the apergion, keeping the wheel in constant and rapid motion.  I had, of course, supplied myself with an ample store of compressed vegetables, preserved meats, milk, tea, coffee, &c., and a supply of water sufficient to last for double the period which the voyage was expected to occupy; also a well-furnished tool-chest (with wires, tubes, &c.).  One of the lower windows was made just large enough to admit my person, and after entering I had to close it and fix it in its place firmly with cement, which, when I wished to quit the vessel, would have again to be removed.

Of course some months were occupied in the manufacture of the different portions of the vessel and her machinery, and sometime more in their combination; so that when, at the end of July, I was ready to start, the opposition was rapidly approaching.  In the course of some fifty days the Earth, moving in her orbit at a rate of about eleven hundred miles [4] per minute, would overtake Mars; that is to say, would pass between him and the Sun.  In starting from the Earth I should share this motion; I too should go eleven hundred miles a minute in the same direction; but as I should travel along an orbit constantly widening, the Earth would leave me behind.  The apergy had to make up for this, as well as to carry me some forty millions of miles in a direction at right angles to the former—­right outward towards the orbit of Mars.  Again, I should share the motion of that particular spot of the Earth’s surface from which I rose around her axis, a motion varying with the latitude, greatest at the equator, nothing at the pole.  This would whirl me round and round the Earth at the rate of a thousand miles an hour; of this I must, of course, get rid as soon as possible.  And when I should be rid of it, I meant to start at first right upward; that is, straight away from the Sun and in the plane of the ecliptic, which is not very different from that in which Mars also moves.  Therefore I should begin my effective ascent from a point of the Earth as far as possible from the Sun; that is, on the midnight meridian.