To accomplish this, a helm was attached to the lower division of the main conductor, by which the latter could be made to move at will in any direction within the limit of its rotation. Controlling this helm was, in the open or steering circle on the right hand, a small knob to be moved exactly parallel to the deviation of the star in the mirror of the metacompass. The left-hand circle, or discometer, was divided by nineteen hundred and twenty concentric circles, equidistant from each other. The outermost, about twice as far from the centre 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.