Reis did, indeed, penetrate to the very heart the principles necessary to be observed in a successful telephone. He was master of the situation. For, as in every practical transmitter in use to-day, so in his transmitter, there was _a loose contact in the circuit so arranged that the voice could act upon it, and thereby regulate the strength of the current_. If you eliminate this part of the apparatus,--screw up the loose-contacts of your transmitters, so that your voices cannot affect them,--what will your telephones be worth? No: the essential principle of the transmitter--“Das Telephon” emphatically as its inventor styled it--is _variable contact_; and that all-essential principle was invented and applied for the purpose of transmitting speech by Philipp Reis in 1861. If this does not suffice as a claim for the invention of the Telephone transmitter, it may well be wondered what will. We can dispense with all other features save this one. We can even dispense with the tympanum or diaphragm which Reis introduced, and can operate on the contact-parts without the intervention of this part of the combination. We can use the very metals which Reis used, and dispense with lamp-black and all the fallacious rubbish that has been subsequently devised about semi-conductors, whatever that term may mean. We can even dispense with springs and adjusting screws. _But with the principle of variable contact we can not dispense._ That which alone is indispensable Philipp Reis discovered. APPENDIX II. ON THE VARIATION OF ELECTRIC RESISTANCE AT A POINT OF IMPERFECT CONTACT IN A CIRCUIT.