| The commutator is an electrical device which gives the possibility to change with extreme easiness the direction of circulation of the elettric current in the part of the circuit which follows it. In this case the electric contact between the fixed and the mobile parts was guaranteed by the mercury, while the device must be placed between the battery and an electric component (a coil, an electro-magnet, etc). Numbering clockwhise the terminals in brass starting from the one on the left, the electric connections must be done as follows: positive pole of the battery, 1, 2, electric device, 4, 3, negative pole of the battery. Then it was sufficient to rotate of 90 degrees the wooden lid to reverse the direction of the current. |