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 conductor 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 more for a complete system of communication such as we now have, was hopeless, so long as frictional electricity was employed, or considerable electrical intensity required. We have now to consider how galvanic electricity, discovered in 1790, was rendered available for telegraphic communication. In the first place, let us consider what galvanic or voltaic electricity is. I have said that electricity can be generated in many ways. It may be said, indeed, that every change in the condition of a substance, whether from mechanical causes, as, for instance, a blow, a series of small blows, friction, and so forth, or from change of temperature, moisture, and the like, or from the action of light, or from chemical processes, results in the development of more or less electricity. When a plate of metal is placed in a vessel containing some acid (diluted) which acts chemically on the metal, this action generates negative electricity, which passes away as it is generated. But if a plate of a different metal, either not chemically affected by the acid or less affected than the former, be placed in the dilute acid, the two plates being only partially immersed and not in contact, then, when a wire is carried from one plate to the other, the excess of positive electricity in the plate least affected by the acid is conveyed to the other, or, in effect, discharged; the chemical action, however, continues, or rather is markedly increased, fresh electricity is generated, and the excess of positive electricity in the plate least affected is constantly discharged. Thus, along the wire connecting the two metals a current of electricity passes from the metal least affected to the metal most affected; a current of negative electricity passes in a contrary direction in the dilute acid.