The recent advances in aërostation, though not radically changing the balloon itself, contribute much to its usefulness and convenience. Improvements have occurred in the means of inflation and deflation, in devices for making topographical and meteorological observations, as also for transmitting and receiving signals. Hydrogen shipped in steel tubes is now available for easy and rapid inflation, the process of obtaining it on a large scale making it practically as cheap as illuminating gas. The ripping panel, invented in 1844 by America’s foremost pioneer aëronaut, John Wise, is a simple and an excellent practical device. This is a long patch running longitudinally above the equator[8] of the balloon, feebly sewed to the envelope, and having a cord, called the “ripping cord,” extending down to the car along the outside or inside of the bag, so that the pilot on coming to earth can let out the gas quickly by tearing a rent in the balloon, thus flattening it promptly on the earth’s surface, so as to avoid dragging and bumping if any wind prevails. During an ascension the rise or fall of the vessel may be instantly noted on the dial of the statoscope, the temperature, pressure and moisture of the atmosphere may be read on recording instruments, messages may be sent by telegraph and telephone either by wire or through space, and sky or landscape may be photographed if there be sufficient light. The bag itself has been improved by making it of special fabrics formed of several layers of silk, or cotton, with thin layers of rubber vulcanized between them to render the cloth impermeable, also the bag, when not designed to cleave the wind, is usually given a spherical form which is the figure of greatest volume for a given surface, the figure originally used by the inventor of the gas balloon; but when designed to be tethered in a wind, it is given a longish shape and a tail so that it may ride the wind like a kite. This type of balloon, though first proposed by Douglass Archibald about 1845, was first made a practical invention by Captain von Sigsfeld and Major von Parseval. In a certain sense it is a tethered motor-balloon, just as a kite is a tethered aëroplane. CHAPTER III EARLY HISTORY OF POWER BALLOONS