A difficulty has been raised by telegraph operators that opening and closing the circuit means opening and closing the circuit in abrupt alternations of make-and-break. Reis never said so. Reis never used the phrase in this restricted and technical sense. He was not a professional telegraphist, and, as pointed out in Appendix I., he so arranged his contacts with the following springs and other contrivances, that the “opening and closing” of the circuit should not and could not be abrupt. A Reis transmitter is no more a “make-and-break” instrument than the Blake transmitter is. Both will give undulatory currents by opening and closing the circuit to a greater or less degree, if spoken gently to. Both will give abrupt makes-and-breaks of the circuit if shouted to, in spite of the following-springs, which are used to prevent abrupt interruptions. The term “opening and closing” which Reis applied to his transmitter, is used by him in exactly the same way as the phrase is used by engineers in describing the action of the governing throttle-valve of a steam-engine. The function of the governor, we are told in treatises on engineering, is to open and close the throttle-valve in a manner corresponding to the fall or rise of the governor-balls. No one in his senses imagines that the opening and closing action here referred to means an absolutely abrupt intermittence in the supply of steam. If the governor-balls rise a little by increase of speed, there is a corresponding closing, proportionate in amount to the amount of rise. If any person were to impress an oscillatory motion of rise and fall upon the governor, the supply of steam would be thrown into corresponding undulations. The matter stands precisely so with Reis’s “interruptor” or “regulator;” it opens and closes the circuit in a manner corresponding with the undulations communicated to it. If it did not, it would violate the principle of correspondence so emphatically laid down by Reis.