Note 1 — CHAPTER 8

Thermometer (thermos, and metron, measure); an instrument for measuring the temperature of the air.—Manometer (manos,and metron, measure); an instrument to show the density or rarity of gases.—Chronometer (chronos. time, and metros, measure) a time measurer, or superior watch—Ruhmkorff's coil, an instrument for producing currents of induced electricity of great intensity. It consists of a coil of copper wire, insulated by being covered with silk, surrounded by another coil of fine wire, also insulated, in which a momentary current is induced when a current is passed through the inner coil from a voltaic battery. When the apparatus is in action, the gas becomes luminous, and produces a white and continued light. The battery and wire are carried in a leather bag, which the traveler fastens by a strap to his shoulders. The lantern is in front, and enables the benighted wanderer to see in the most profound obscurity. He may venture without fear of explosion into the midst of the most inflammable gases, and the lantern will burn beneath the deepest waters. H. D. Ruhmkorff, an able and learned chemist, discovered the induction coil. In 1864 he won the quinquennial French prize of £2,000 for this ingenious application of electricity—A voltaic battery, so called from Volta, its designer, is an apparatus consisting of a series of metal plates arranged in pairs and subjected to the action of saline solutions for producing currents of electricity.