Electric heater

Claim 1

AN ELECTRIC HEATER COMPRISING A BODY MADE OF A SYNTHETIC MOLDABLE PLASTIC MATERIAL NON-ADHESIVE AT ATMOSPHERIC PRESSURE AT TEMPERATURE RANGING FROM -40* C. TO +80*C., SAID BODY BEING OF SLIGHT THICKNESS AS COMPARED WITH ITS REMAINING DIMENSIONS AND CONSISTING OF A PLATE, SAID PLATE BEING FORMED OF A PLURALITY OF SHEETS, THE UPPER AND LOWER SHEETS BEING FLAT ON THEIR OUTER SURFACE AND HAVING TRANSVERSAL PROJECTIONS ON THEIR INNER SURFACES, THE INTERMEDIATE SHEETS HAVING TRANSVERSAL PROJECTION ON BOTH SURFACES, THE PROJECTIONS IN ONE SHEET BEING ADAPTED TO BE COUPLED TO THE PROJECTIONS IN THE ADJACENT SHEET, EACH TWO ADJACENT SHEETS DEFINING BETWEEN THEMSELVES A PLURALITY OF DUCTS CONNECTED ONE TO ANOTHER, SAID DUCTS BEING REGULARLY DISTRIBUTED OVER THE BODY AND DISPOSED ON SEVERAL LEVELS, TIGHT COVERING MEANS DEFINING TOGETHER WITH SAID SHEETS A SEALED TIGHT INNER SPACE INCLUDING SAID DUCTS, AN ELECTRICAL RESISTANCE IN EACH LEVEL OF DUCTS, EACH ELECTRICAL RESISTANCE BEING LOOSE WITHIN SAID INNER SPACE AND BEING FIXED TO SAID BODY ONLY AT ITS TWO ENDS, THE SAID ELECTRICAL RESISTANCE BEING DISPOSED ALONG ALL THE PATH DEFINED BY SAID DUCTS AND BEING ADAPTED TO EXPAND FREELY IN SAID DUCTS, THE LENGTH, CROSS-SECTION AND RESISTIVITY OF THE ELECTRICAL RESISTANCE BEING SUCH THAT THE MAXIMUM TEMPERATURE ATTAINABLE IN OPERATION IS SUBSTANTIALLY LESS THAN THE SOFTENING TEMPERATURE OF THE PLASTIC MATERIAL CONSITUTING THE BODY, THE SAID ENDS OF THE ELECTRICAL RESISTANCE BEING PROVIDED WITH CONNECTING MEANS ADAPTED TO BE CONNECTED TO THE SOURCE OF ELECTRIC CURRENT, AND A SELECTOR SWITCH ADAPTED TO CONNECT AT ALL EACH ELECTRICAL RESISTANCE IN SERIES WITH THE OTHER ELECTRICAL RESISTANCES.