593,708. Recording- apparatus. KEINATH, G. March 16, 1945, No. 6709. Convention date, Feb. 12,1944. [Class 106 (iv)] [Also in Groups XXXVI and XXXVIII] A system for recording a number of variable quantities comprises a number of gauge elements connected in turn by a selective contact device to an adjustable impedance, which is operated with an indicating means bearing a number of symbols, so that when the impedance device is adjusted to a magnitude indicative of that to be measured, the appropriate symbol is exhibited and an image thereof is recorded. Fig. 1 shows a number of thermocouples connected in turn by a selector switch SS through an amplifier 141 and control relay CR to the continuously driven slide contact 173 of a potentiometer 171. When the slide contact passes through the position at which the voltage across the potentiometer balances the amplifier output, the contact device of relay CR. switches from one position to the other causing condenser 163 to discharge through lamp L. An indicating member 176 carrying a number of symbols on its periphery and rotated with the slide contact is thus illuminated at the instant at which the figure corresponding to the quantity to be measured appears at the window 168 and a photographic record is made on a film 191. The record also includes the indications of a counting device NS, to show which thermocouple is being measured and of a clock. At the end of each revolution, a contact 183 on the slider engages contact 181 producing an impulse which operates the ratchet-andpawl mechanism 107, 108 to drive the selector switch on one step, operates the counting device NS to advance it one step and operates ratchet-and-pawl mechanism 197, 198 to drive the film into its next position, the cycle of operations then being repeated for the next thermocouple. The system shown in Fig. 6 is designed for use with bolometric amplifiers which operate on a thermo-electric principle and have a relatively large time constant. The stepping switch is shown with three banks of contacts and each thermocouple is connected to three consecutive contacts of a bank, the contact arm of each bank being displaced by one contact from the next. Thus, each thermocouple is connected to an amplifier during an interval three times as long as a single stepping period of the selector switch. A connection is established between an amplifier and the potentiometer through a commutator 256 only when the movable member of the selector switch reaches the last contact of a group by which time the amplified voltage has attained its correct value. The commutator is driven in steps by impulses produced when contact 283 on the potentiometer slider engages contact 281, the recording device being driven through gearing 258. In this modification, the symbols are inked by an inking device 260, and the ink from the symbol adjacent the recording strip is transferred by an electrostatic effect to the strip when condenser 263 discharges. In a modification, Fig. 9 (not shown), the gauges are resistance elements and are connected in turn in one arm of a Wheatstone bridge, another arm of which is continuously varied. In other modifications, Figs. 10, 11 (not shown), and Fig. 12 (not shown), the adjustable impedance comprises a variable condenser or inductance and involves a resonance method for measuring the various quantities. In a further modification, Figs. 13 and 14, in which the gauge readings are transmitted, e.g. from an aeroplane, by radio to a distant recording station, the gauge elements G1... G4 generate alternating currents which are rectified and applied to one winding of a differential relay, the other winding of which has its excitation continuously varied. At the beginning of each cycle, a reference impulse is sent over winding S2 of transformer TR and at the moment of balance, another impulse over winding S1. These impulses have different frequencies and are separated at the receiver by filters F1, F2, 'the measuring impulse causing a lamp L to flash and the reference impulse operating a start-stop drive for the indicating drum 676 and energizing the counter NS.