1. APPARATUS COMPRISING IN COMBINATION, A CHAMBER; AN ORIFICE LEADING TO SAID CHAMBER; A HEATING SHELL SURROUNDING SAID CHAMBER AND ADAPTED TO SUPPLY HEAT TO SAID CHAMBER; INSULATION SURROUNDING SAID SHELL; TEMPERATURE SENSITIVE MEANS WITHIN SAID CHAMBER; A HEAT BALANCING CIRCUIT CONTROLLED BY SAID TEMPERATURE SENSITIVE MEANS FOR SUPPLYING POWER TO SAID HEATING SHELL TO MAINTAIN SAID CHAMBER AT SUBSTANTIALLY A CONSTANT TEMPERATURE; A MASS INCLUDING AN ELASTOMERIC BODY COMPRISING A POLYMER AND A FLUID WITHIN SAID CHAMBER; AND CONTACTS ADAPTED TO BE ACTUATED BY THE VARIATION IN VOLUME OF SAID ELASTOMERIC BODY DUE TO THE AMBIENT PRESSURE REACHING THE BOILING PRESSURE OF SAID FLUID.