But the greatest improvement in aerial telegraphy was made during the French Revolution by Claude Chappe, a Frenchman living in Paris. In 1793, Chappe erected on the roof of the palace of the Louvre a post at the top of which was a cross-beam which moved on a pivot about the center like a scale beam (Fig. 7). The cross-beam could be moved horizontally, vertically or at almost any angle by means of cords. Chappe invented a number of positions for these arms and each position stood for a certain letter of the alphabet. Machines of this kind were erected on towers at places from nine to twelve miles apart and soon Chappe was sending messages from Paris to the city of Lille, 130 miles away. The messages were sent with great rapidity, for they passed from one tower to another with the velocity of light--about 185,000 miles a second--and it was possible for the operator to spell out about 100 words in an hour. And Chappe's messages could be sent at any time, day or night, for the arms of the machine were furnished with Argand lamps for night work. Chappe's invention was the greatest which had thus far been made in the history of the message. The new system of telegraphy proved to be entirely successful and practical and it was not long before machines similar to those invented by Chappe were in use in England and other countries. In 1828, an English writer had the following words of praise for aerial telegraphy: "Telegraphs have now been brought to so great a degree of perfection that they carry information so speedily and distinctly and are so much simplified that they can be constructed and maintained at little expense. The advantages, too, which result from their use are almost inconceivable. Not to speak of the speed with which information is communicated and orders given in time of war, by means of these aerial signals the whole kingdom could be prepared in an instant to oppose an invading enemy." [Illustration: FIG. 8.--STURGEON ELECTRO-MAGNET, 1825.]