A non-invasive measurement system for measuring the electrical potential of a voltage source includes a sensing electrode spaced from the voltage source. The network contains a plurality of network devices and offers a set of services to subscribers. The circuitry includes a signal processing unit in communication with each of the taps, wherein the signal processing unit is configured to control a phase for at least a portion of a signal for at least a first of the taps relative to a phase for a corresponding portion of the signal for at least a second of the taps. The slings are fastened to an outer side surface of the front wall. In the optical apparatus, one surface of the optical device in which the photoreceptorlight-emitting region is formed and one surface of the transparent member are arrange so as to face to each other and electrodes of the optical device and the protruding electrodes of the transparent member are electrically connected and also adhered by the transparent adhesive.