Electricity, then, positive or negative, however generated, passes freely along conducting substances, but is stopped by an insulating body, just as light passes through transparent substances, but is stopped by an opaque body. Moreover, electricity may be made to pass to any distance along conducting bodies suitably insulated. Thus, it might seem that we have here the problem of distant communication solved. In fact, the first suggestion of the use of electricity in telegraphy was based on this property. When a charge of electricity has been obtained by the use of an ordinary electrical machine, this charge can be drawn off at a distant point, if a conducting channel properly insulated connects that point with the bodies (of whatever nature) which have been charged with electricity. In 1747, Dr. Watson exhibited electrical effects from the discharges of Leyden jars (vessels suitably constructed to receive and retain electricity) at a distance of two miles from the electrical machine. In 1774, Le Sage proposed that by means of wires the electricity developed by an electrical machine should be transmitted by insulated wires to a point where an electroscope, or instrument for indicating the presence of electricity, should, by its movements, mark the letters of the alphabet, one wire being provided for each letter. In 1798 Béthencourt repeated Watson’s experiment, increasing the distance to twenty-seven miles, the extremities of his line of communication being at Madrid and Aranjuez. (Guillemin, by the way, in his “Applications of the Physical Forces,” passes over Watson’s experiment; in fact, throughout his chapters on the electric telegraph, the steam-engine, and other subjects, he seems desirous of conveying as far as possible the impression that all the great advances of modern science had their origin in Paris and its neighbourhood.)