Gramme ring armature for dynamo--Gramme, France, 1868. Theory that light consists of electromagnetic waves--Clerk-Maxwell, England, 1873. Quadruplex telegraph, sending four messages over one wire at the same time--Edison, 1873. Siphon recorder for submarine telegraph, sensitive to very feeble currents--Sir William Thomson, England, 1874. Telephone, varying current, first practical working telephone--Alexander Graham Bell, United States, 1876. Electric candle, beginning of present arc light--Paul Jablochkoff, Russia, 1876. Telephone transmitter of variable resistance--Emil Berliner and Edison working independently, United States, 1877. Edison used carbon contacts, Berliner used metal contacts. Brush system of arc lighting--1878. Incandescent electric lamp with carbon filament--Edison, 1878. First electric locomotive--Siemens, Germany, 1879. Blake telephone transmitter--Blake, United States, 1880. Storage battery, lead grids filled with active material--Faure, France, 1881. Electric Welding--Elihu Thompson, United States, 1886. Electric Waves discovered by experiment--Heinrich Hertz, Germany, 1888. Coherer for receiving electric Waves--Edward Branly, France, 1890. X-rays--Discovered by Prof. W. C. Roentgen, Germany; announced to the public in 1895. Wireless telegraphy--G. Marconi, Italy, 1896. Nernst electric light, a clay capable of conducting electricity when heated is used; it becomes incandescent without a vacuum--Walter Nernst, Germany, 1897. Radium discovered by Madame Curie, France, 1898. Explosives Gunpowder--Inventor and date unknown. Guncotton--Schönbein, Germany, 1845. Nitroglycerine--Sobrero, 1847. Explosive gelatine--A. Nobel, France, 1863. Dynamite--A. Nobel, France, 1866. Smokeless powder--Vielle, France, 1866. Firearms and Ordnance Spirally grooved rifle barrel--Koster, England, 1620. Breech-loading shot-gun--Thornton and Hall, United States, 1811. The revolver; a device "for combining a number of long barrels so as to rotate upon a spindle by the act of cocking the hammer"--Samuel Colt, United States, 1836. Breech gun-lock, interrupted thread--Chambers, United States, 1849. Magazine gun--Walter Hunt, United States, 1849. Breech-loading rifle--Maynard, United States, 1851. Iron-clad floating batteries first used in Crimean War--1855. Breech-loading ordnance--Wright and Gould, United States, 1858. Revolving turret for floating batteries--Theodore Timby, United States, 1862. First iron-clad floating battery propelled by steam: the _Monitor_--John Ericsson, United States, 1862. Gatling gun--Dr. R. J. Gatling, United States, 1862.