contributor to experimental investigation, and he also called attention to the resemblance between the electric spark and lightning. The most ardent student of electricity in the early years of the eighteenth century was Stephen Gray. He performed a multitude of experiments, nearly all of which added something to the rapidly accumulating stock of knowledge, but doubtless his most important contribution was his discovery of the distinction between conductors and non-conductors. ... Some of Gray's papers fell into the hands of Dufay, an officer of the French army, who, after several years' service, had resigned his post to devote himself to scientific pursuits. ... His most important discovery was the existence of two distinct species of electricity, which he named 'vitreous' and 'resinous.' ... A very important advance was made in 1745 in the invention of the Leyden jar or phial. As has so many times happened in the history of scientific discovery, it seems tolerably certain that this interesting device was hit upon by at least three persons, working independently of each other. One Cuneus, a monk named Kleist, and Professor Muschenbroeck, of Leyden, are all accredited with the discovery. ... Sir William Watson perfected it by adding the outside metallic coating, and was by its aid enabled to fire gunpowder and other inflammables." _T. C. Mendenhall, A Century of Electricity, chapter 1._ ELECTRICITY: A. D. 1745-1747. Franklin's identification of Electricity with Lightning.