Mr. John Wise, the well-known aeronaut, says: "There are two ways of preparing linseed-oil for balloon varnish: the quick and the slow process. The first is by heating the oil up to a temperature at which it will ignite spontaneously. In order to secure it from burning up, it must be heated in an iron or copper vessel, with a lid that can be closed when it begins to emit dense white vapor. If it is desired to have it fast drying, from 4 to 6 oz.s. litharge per gallon should be boiled in it. This process takes about one hour, and renders the oil thick and tough, giving a good body and glossy surface to he cloth. The slow process is to boil the oil from 12 to 20 hours, keeping it at a temperature of about 200 Fahr., incorporating with it, while boiling, 1/2 oz. sulphate of manganese to each gallon of oil. These varnishes should be applied to the cloth tolerably hot. There are other formulas, such as the incorporation with the oil of some birdlime. Gum-elastic is also used to give the oil body and elasticity. When I desire to make a balloon extraordinarily close, I give it a first coating of compound varnish made up of equal parts white glue and glycerine."