The high tension current is supplied from an apparatus of a special type E with which a current as high as 100,000 volts can be obtained. Another prominent feature is the high tension interrupter D, which cuts the electric circuit of the tube in and out, in synchrony with the camera mechanism. Thus the Crookes tube is active while the shutter is open but inactive while it is closed.
This interrupter consists of a small glass vessel, charged with petrol, and sealed with a cover of insulating material. Within the vessel, and spaced about 2 inches apart, are two brackets, which extend through the sides of the receptacle through hermetically sealed joints. To these brackets the positive and negative wires are coupled. Above the brackets, and moving within the vessel, is an inverted U-shaped piece. This slides up and down through apertures provided for the purpose in the insulated cover. When lowered to its full extent the arms rest upon the brackets, to which the wires are attached, and this contact completes the electrical circuit. A pulley wire is fixed to the centre of the inverted U-piece to allow it to be moved up and down as required. The up-and-down movement serves as a make-and-break for the circuit. A lift of a quarter of an inch suffices to break the circuit, which lift is effected by the mechanism of the camera over a system of cords and pulleys. Thus, when the camera handle is turned to open the shutter, the contact piece in the interrupter is lowered, the circuit is completed, and the Crookes tube is brought into use. Directly the shutter is closed the contact piece is raised and the tube is disconnected. This simple control permits the exposure to be varied from five or six to sixteen exposures per second, while the tube can be kept continuously at work for as many as fifty-five seconds if desired.
The camera is fitted with a lens made from quartz, which permits the maximum quantity of the actinic rays to pass through to the sensitized film. The film is covered with an exceptionally sensitive emulsion in order to ensure the best results possible with very short exposures. In order to protect the spools of film in the camera from the actinic properties of the rays diffused from the fluorescent screen, the boxes are covered with sheet lead, while the operator is protected with a lead apron, such as is used generally in Röntgen ray investigations.
The many interesting films which Dr. Comandon has produced offer adequate testimony to the practicability and success of the system which he has evolved. Undoubtedly it is the simplest and most inexpensive method of "radio-cinematography" which has been brought into practical operation up to the present, and it is one which may be followed by the private investigator with such modifications as may suggest themselves in particular cases.