The progress of chemical science led to the discovery of an inexhaustible supply of force, which combines all the advantages of small cost, extreme portability, resistless strength, immunity from risk, and universal applicability. All this was obtained by the steady work and indomitable perseverance of three chemists who, contrary to usage, devoted themselves to this one branch of science for several consecutive cyclical periods of their career. Not being skilled in chemical learning, I was unable to comprehend the nature of their discovery; but I was told that it consisted in the application of certain laws of combination among various gases, each of which is easy to manufacture and store up. CHAPTER VII. Of the first attempt to pass the Equatorial Tornado; and its tragical issue—Of the attempt to pass the Cloud-Screen. These improvements in ship-building and ship-propelling were naturally followed by a great development of the science of navigation, to which the mathematical powers of the Hesperians formed an invaluable auxiliary. And thus all that was possible for them to ascertain concerning the physical universe was soon learned. The circumnavigation of the globe was easily effected, for the shape of the continent was such that it could be made without going out of sight of land. Other and more adventurous ships were sent on voyages of discovery in a southerly direction, and these made the discovery of the frightful tempest, mentioned before, which rages everlastingly in the equatorial zone. Not one of these ships succeeded in getting within two hundred miles of the equator itself. The crews reported unanimously that, even at that distance, the seas were simply terrific, and appeared to increase rapidly in violence towards the south. Some of them escaped from the vortex with extreme difficulty.