The idea of using electricity as motive power on railroads is nearly as old as the railroads themselves. In 1837, when the utility of steam for purposes of transportation was doubted, Robert Davidson propelled a car with an electric engine on the Edinburgh and Glasgow road. In the fifties Thomas Davenport, a Vermont blacksmith, constructed an electric engine containing all the essential elements of the modern electric motor. Little progress, however, was made in the use of electricity for motive power, because the cost of producing the electric current was so great. In 1887 Lieut. Sprague, overcoming most of the difficulties then existing, installed at Richmond, Virginia, the first successful electric railway in the world. Managers of street railways in other cities visited Richmond, and after an inspection of what Sprague had done there, decided to substitute electricity for animal power. No other construction has had a more rapid growth since the time of its invention than the electric railway. In 1890 there were only thirteen unimportant electric roads. Now there is hardly a city of the civilized world where the hum of the electric street car is not heard at all hours of day and night. Modern urban life could scarcely exist without it. It is rapidly pushing its way into the country and giving the farmer the privilege of rapid and cheap transit. The uses of electricity are by no means exhausted in the four major inventions of the telegraph, the telephone, the electric light, and the electric street car. It has been put to many minor uses. Among the most interesting and important of these are the Roentgen or X-rays, discovered by Wilhelm Konrad von Roentgen, a German physicist, in 1895. They were named X-rays by their discoverer, because the ultimate nature of their radiation was unknown, the letter X being commonly used in algebra to represent an unknown quantity. The X-rays are peculiar electric rays having the power to penetrate wood, flesh, and other opaque substances. They are of much value to surgery in disclosing the location of bullets, foreign substances of various kinds, and other objective points in the interior of the human body. The United States government has demonstrated through its Department of Agriculture that electricity applied to the soil will quicken and help the growth of certain vegetables. It has also shown that certain crops are forwarded by the application of electric light. The New York legislature in 1888 passed a law providing that criminals should be executed in that state thereafter by electrocution, that is, by sending through the body of the condemned person, a current of electricity strong enough to produce death. Execution in this way makes death quicker and apparently less painful than by hanging, the method used previously, and subsequently several other states have passed laws for electrical execution, following the example of New York.