The late Clerk Maxwell, when asked by a distinguished scientist what was the greatest scientific discovery of the last half-century, replied: "That the Gramme machine is reversible." In other words, that power will not only produce electricity, but that electricity will produce power. By turning a big wheel at Niagara we can produce an electric current that will turn another wheel for us fifty, or perhaps five hundred miles away. The dynamo is one of the great achievements of the day to which Charles F. Brush, of Cleveland, O., has devoted himself with much signal success. Brush was born in March, 1849, in Euclid Township near Cleveland, and his early years were spent on his father's farm. When fourteen years old he went to the public school at Collamer, and later to the Cleveland High-school, and as early as 1862 distinguished himself by making magnetic machines and batteries for the high-school. During his senior year in the high-school, the chemical and physical apparatus of the laboratory of the school was placed under his charge. In this year he constructed an electric motor having its field magnets as well as its armature excited by the electric current. He also constructed a microscope and a telescope, making all the parts himself, down to the grinding of the lenses. He devised an apparatus for turning on the gas in the street-lamps of Cleveland, lighting it and turning it off again. When he was eighteen years of age he entered Michigan University at Ann Arbor, and, following his particular bent, was graduated as a mining engineer in 1869, one year ahead of his class. Returning to Cleveland he began work as an analytical chemist and soon became interested in the iron business. In 1875 Brush's attention was first called to electricity by George W. Stockly, who suggested that there was an immense field ready for a cheaper and more easily managed dynamo than the Gramme or Siemens, the best types then known. Stockly, who was interested in the Telegraph Supply Company, of Cleveland, agreed to undertake the manufacture of such a machine if one was devised. In two months Brush made a dynamo so perfect in every way that it was running until it was taken to the World's Fair in 1893. Having made a good dynamo, the next step was a better lamp than those in use. Six months of experimenting resulted in the Brush arc light. Stockly was so well satisfied with the commercial value of these inventions that the Telegraph Supply Company, a small concern then employing about twenty-five men, was reorganized in 1879, as the Brush Electric Company. In 1880 the Brush Company put its first lights into New York City, and it has since extended the system until there is scarcely a town in the country where the light may not be found. Besides dynamos and lamps, the immense establishment at Cleveland employs its twelve hundred men in making carbons, storage-batteries, and electro-plating apparatus. Mr. Brush is a self-taught mechanic, able to