Helium refrigerator

Claim 1

IN COMBINATION WITH A HELIUM REFRIGERATOR OF THE TYPE INCLUDING A LOW-TEMPERATURE COUNTER-FLOW HEAT EXCHANGE ADAPTED TO BE SUBSTANTIALLY FILLED WITH HELIUM IN A GASEOUS STATE AS WELL AS IN A LIQUID STATE, ENCASED IN A RELATIVELY THIN EXTERNAL JACKET FORMED OF THERMALLY CONDUCTIVE MATERIAL AND HAVING A MAXIMUM REVERSE COOLING CAPACITY WHEN THE HEAT EXCHANGER IS SUBSTANTIALLY FILLED WITH LIQUID HELIUM AND MINIMUM RESERVE COOLING CAPACITY WHEN THE HEAT EXCHANGER IS SUBSTANTIALLY FILLED WITH HELIUM IN A GASEOUS STATE, MEANS FOR PROVIDING A CONTINUOUS INDICATION OF THE RESERVE COOLING CAPACITY OF SAID REFRIGETOR, INCLUDING: A. A PAIR OF MUTALLY SPACED ELECTRICAL RESISTORS MOUNTED IN SPACED RELATION ON THE EXTERNAL SURFACE OF SAID JACKET, NEAR THE UPPERMOST END THEREOF, EACH BEING CHARACTERIZED BY A LOGARITHMIC COEFFICIENT OF RESISTANCE INVERSELY PROPORTIONAL TO TEMPERATURE, AND B. CIRCUIT MEANS FOR CONTINUOUSLY PROVIDING INTELLIGENCE INDICATIVE OF TEMPERATURE INDUCED CHANGES IN THE DIFFERENTIAL IN THE ELECTRICAL CONDUCTIVELY OF SAID PAIR OF RESISTORS INCLUDING, MEANS CONNECTING SAID PAIR OF RESOSTORS IN ELECTRICAL PARALLELISM WITHIN A COMMON ELECTRICAL BRIDGE CIRCUIT, MEAND FOR SIMULTANEOUSLY APPLYING A COMMON VOLTAGE ACROSS SAID RESISTORS, AND MEANS INCLUDING A VOLTMETER CONNECTED BETWEEN SAID RESISTORS FOR COMPARING TEMPERATURE INDUCED CHANGES IN VOLTAGE DROPS ACROSS THE RESISTORS OF SAID PAIR.