Beneath the centre of the Balloon, and about two-thirds of its length, is a frame of light wood, answering to the hoop of an ordinary Balloon; to which are attached the cords of the net which encloses the suspending vessel, and which serves to distribute the pressure of the appended weight equally over its whole surface, as well as to form an intermediate means of attachment for the rest of the apparatus. This consists of a car or basket in the centre; at one end the rudder, and at the other the Archimedean Screw. The car is about two feet long and eighteen inches broad, and is laced to the hoop by cords, which running through loops instead of being fastened individually, allow of unlimited play, and equalize the application of the weight of the car to the hoop, as of the whole to the Balloon above. The Archimedean Screw consists of an axis of hollow brass tube eighteen inches in length, through which, upon a semi-spiral of 15° of inclination, are passed a series of radii or spokes of steel wire, two feet long, (thus projecting a foot on either side) and which being connected at their outer extremities by two bands of flattened wire, form the frame work of the Screw, which is completed by a covering of oiled silk cut into gores, and tightly stretched, so as to present as nearly uniform a surface as the nature of the case will permit. This Screw is supported at either end of the axis by pillars of hollow brass tube descending from the hoop, in the lower extremities of which are the holes in which the pivots of the axis revolve. From the end of the axis which is next the car, proceeds a shaft of steel, which connects the Archimedean Screw with the pinion of a piece of spring machinery seated in the car; by the operation of which it is made to revolve, and a progressive motion communicated to the whole apparatus. This spring is of considerable power compared with its dimensions, being capable of raising about 45 pounds upon a barrel of four inches diameter after the first turn, and gradually increasing as it is wound up. It weighs altogether, eight pounds six ounces.