ON SOME MARVELS IN TELEGRAPHY. 239 



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 elec- 

 trical 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 

 Be'thencourt repeated Watson's experiment, increasing the dis- 

 tance to twenty-seven miles, the extremities of his line of com- 

 munication 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 sub- 

 jects, 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.) 



From Watson's time until 1823 attempts were made in 

 this country and on the Continent to make the electrical 

 machine serve as the means of telegraphic communication. 

 All the familiar phenomena of the lecture-room have been 

 suggested as signals. The motion of pith balls, the electric 

 spark, the perforation of paper by the spark, the discharge of 

 sparks on a fulminating pane (a glass sheet on which pieces 

 of tinfoil are suitably arranged, so that sparks passing from 

 one to another form various figures or devices), and other 

 phenomena, were proposed and employed experimentally. 

 But practically these methods were not effectual. The 

 familiar phenomenon of the electric spark explains the cause 

 of failure. The spark indicates the passage of electricity 

 across an insulating medium dry air when a good con- 

 ductor approaches within a certain distance of the charged 

 body. The greater the charge of electricity, the greater is 

 the distance over which the electricity will thus make its 

 escape. Insulation, then, for many miles of wire, and still 



