The making of the net of the balloon is another part of the work which must be delegated to professionals. The material point is that the net distributes the weight evenly over the surface of the upper hemisphere of the envelope. The strength of the cordage is an item which must be carefully tested. Different samples of the same material show such wide variations in strength that nothing but an actual test will determine. In general, however, it may be said that China-grass cordage is four times as strong as hemp cordage, and silk cordage is ten times as strong as hemp--for the same size cords. The meshes of the net should be small, allowing the use of a small cord. Large cords mean large knots, and these wear seriously upon the balloon envelope, and are very likely to cause leaks. In large meshes, also, the envelope puffs out between the cords and becomes somewhat stretched, opening pores through which much gas is lost by diffusion. The “star,” or centre of the net at the apex of the balloon, must be fastened immovably to the rim of the valve. The suspension cords begin at from 30° to 45° below the equator of the envelope, and are looped through rings in what are called “goose-necks.” These allow a measure of sliding motion to the cordage as the basket sways in the wind. For protecting the net against rotting from frequent wetting, it is recommended to saturate it thoroughly with a solution of acetate of soda, drying immediately. Paraffin is sometimes used with more or less success, but tarring should be avoided, as it materially weakens the cordage. Oil or grease are even worse. At the bottom of the net proper the few large cords into which the many small cords have been merged are attached to the ring of the balloon. This is either of steel or of several layers of wood well bound together. The ropes supporting the basket are also fastened to this ring, and from it hang the trail-rope and the holding ropes. [Illustration: Sketch showing the diamond mesh of balloon cordage and the method of distributing the rings for the goose-necks; also the merging of netting cords into the suspension cords which support the car. The principal knots used in tying balloon nets are shown on the right.]