This sphere, fitted with two lateral regulating valves, one lower automatic valve, and a “rending flap,” measures 22 yards in diameter, by 1,431 yards surface; it is enclosed in a net of hemp cord, terminating in systems of “crow feet,” and suspending ropes attached to the car by means of a “load ring.” The upper part of the balloon is protected against rain and snow by a varnished silk cover, the apex of which is fixed to the upper pole of the envelope, and the lower margin to the meshes of the net. THE ENVELOPE.—In making up the envelope, 600 pieces of best quality Pongee silk, each from 18 to 19 yards long by about 18 inches wide, were used. From each of these a piece was cut off which was tried in both directions—that of the chain and that of the weft; then the pieces were classified according to their strength, in order to be subjected to the operation of cementing or joining together. All these pieces, after being cemented together, were tried again before being used. The trials were made by means of a Perreaux dynamometer, with strips about 2 inches wide by 4 inches long, under the control of Messrs. P. de Nordenfeld and Noël, engineers of the Nordenfeld Company, to whom Andrée had entrusted the task of testing the materials used in the construction of his balloon. [Illustration: VIEW OF THE LOWER PART OF THE BALLOON.] The tests gave the following results:—For double tissue, the breaking strains varied from 5,291 lbs. to 7,936 lbs. per yard, for threefold tissue from 6,854 to 12,125, and for fourfold tissue, made up of the best single pieces found, from 13,227 to 15,873 lbs. per yard. The minimum resistance demanded by Andrée was fixed at 2,204 lbs. per yard and per single thickness of Pongee. This minimum was therefore greatly exceeded. The cemented pieces were classified according to their strength, for distribution over the surface of the balloon as the strain demanded. The upper part of the envelope is a disc 19 feet 8 inches in diameter, formed by twenty-four widths of fourfold silk. The adjoining part, consisting of threefold silk up to 13 feet 1 inch below the equator of the sphere, is composed of forty-one zones made up of forty-eight widths each. The remainder of the balloon, down to the lower parallel, having a diameter of 23 feet, is of double material, being made up of twenty-two zones of forty-eight widths; and finally the lower part, including the appendage, is of threefold silk, and consists of five zones of forty-eight widths, and three zones of twenty-four widths each. The portions made up of threefold and double Pongee are joined together by an intermediate zone in which the various widths of material are alternately made up, half of threefold and half of double tissue.