487 Findings of Fact 24. The structure as defined by claim 21 and a selective control valve intermediate said manifold and said first named means whereby the heating fluid may be selectively directed to various portions of said surface. 25. The structure as defined in claim 21 wherein said ducts forming part of said surface include a corrugated sheet of material secured to said surface at intervals to thereby form passages for the heating fluid. 26. The structure as defined in claim 21 wherein the first means is thermally insulated from the interior of the wing. 27. The structure as defined in claim 21 wherein means are disposed in the zone of rarefaction and facing to the rear of the direction of motion of said aeroplane structure for ejecting heating fluid from said ducts. 6. The claims relied on all recite airplane structure comprising an exposed surface or sheet and a plurality of heating ducts formed in part or defined by said surface. Claims 1, 2, 3 and 19 recite that the ducts are secured to or are internal to the undersurface of the exposed surface. Claims 1, 19, 21 and 23-27 recite that the ducts are parallel. Claims 2, 3, 16, 17, 19, 21 and 23-27 recite that the ducts are spaced from one another. Claims 1, 19, 21 and 23-27 recite the airplane structure as a wing. Claims 2 and 3 specify that the ducts are imperforate and in intimate heat transferring relation to the exposed surface. Claims 19, 21 and 23-27 add a recital of a manifold for supplying a heating fluid to the heating ducts. Claim 24 includes a selective control valve, claim 25 specifies that the ducts include a corrugated sheet, claim 26 specifices that the ducts are thermally insulated from the interior of the wing, and claim 27 includes means facing rearward for ejecting heating fluid from the heating ducts. The claims include various functional statements and whereby clauses reciting that the distance between ducts is such that all of the exposed surface is maintained at a temperature above freezing, or reciting that the surface is heated by the direct application of heat, or reciting that the surface lying between ducts is heated by linear conduction of heat, or reciting that the surface is in effect divided into portions supplied with heat from different ducts. Findings of Fact 136 C. Cls. 7. The Smith patent specification states that the invention provides a construction to distribute engine exhaust gases into effective heat exchange relation to substantially the entire upper wing surfaces and to desired portions of the fuselage. It states that it provides for discharging the engine exhaust gases in zones of negative pressure to induce the flow of gases through the heating ducts without increasing the back or exhaust pressure on the engine. It states that the chamber 13 extending across the forward portion of the wing varies in effective width to compensate for the falling off in volume of the exhaust gases delivered to wing areas toward the outer end of the wing. It states that although the chamber 13 is illustrated at one edge of the wing 2, it is to be understood that the positioning of chamber 13 and the shape and direction of the distributing ducts 12 may be varied as desired. It states that the ducts 12 terminate in ports 18 in hoods 19 preferably placed near the forward edge of the wing. It further states that the upper surface 20 of the wing 2 preferably is made of metal such as aluminum and its alloys, and that the heating ducts 12 are formed by welding or riveting metallic troughs to the undersurface of the sheet constituting the surface 20. 8. The Smith patent specification does not disclose or mention sizes of manifolds, chambers, or the heating ducts; does not disclose or mention the temperature range of the exhaust gases or the temperature of heated surfaces necessary to prevent icing, and does not mention or suggest the use of hot air and gases produced by a combustion heater and circulated by pressures produced by a ram air scoop. There is no mention in the Smith patent specification of the theory of uniform forced convection heat transfer, and no mention of the Reynolds Number method of flow analysis. 9. The Smith patent specification does refer to and recognize prior efforts to prevent icing by the application of oil to the exposed surfaces of airplanes, and by the discharge of exhaust gases directly into the hollow body of an airplane wing. 487 Findings of Fact 10. A preferred embodiment of the Smith patent construction is illustrated in Figures 1-5, 9 and 10 of the patent drawings. Three modified forms of heating duct constructions are illustrated in Figures 6, 7 and 8, respectively. A modified form of control valve is illustrated in Figure 11, and a modified form of port construction is illustrated in Figures 12 and 13. 11. Claim 1 of the Smith patent may be read in the following manner upon the structures illustrated in Figures 1–5 of the patent drawings: An aeroplane wing [3] comprising an upper surface [20 on Figure 5] and a plurality of substantially parallel heating ducts [12] secured to the undersurface thereof, whereby in effect a substantially continuous body of heated fluid [exhaust gases from engine 7] is applied to the undersurface only of said aeroplane surface [20], said ducts [12] being formed in part by said surfaces [20]. 12. Other claims in suit may be read upon the structures illustrated in a similar manner to that given above for claim 1. The heating ducts 12 are shown secured to and internal to the undersurface of the exposed wing surface 20. The heating ducts 12 are illustrated as parallel. The ducts 12 are shown spaced from one another in Figure 5. The drawings show an airplane wing 3, and show ducts 12 in intimate heat transferring relation to the exposed surface 20. A manifold or header 13 is shown for supplying a heating fluid to the heating ducts 12. The selective control valve recited in claim 24 is illustrated in Figure 3 as slidable plates 12a. Heating ducts formed by corrugated sheets are shown in Figures 6, 7 and 8. The thermal insulation recited in claim 26 is shown by the numeral 22 in Figure 5. The heating fluid ejecting means recited in claim 27 is shown as hoods 19 in Figures 1, 2, 3 and 4, and as hood 24 in the modification illustrated in Figures 12 and 13. 13. There is no evidence that the plaintiff Smith reduced his alleged invention to practice prior to his constructive reduction to practice on April 5, 1929, the filing date of his application for United States Letters Patent. 136 C. Cls. Findings of Fact PRIOR ART 14. Disclosures of structures pertinent to the Smith patent construction and prior in date to the April 5, 1929, filing date of the Smith application include the following items arranged by date: a. British patent 3331 of 1911 to Sueter, accepted February 8, 1912, taught a thermal anti-icing system including leading a regulated quantity of exhaust gases into metal tubes in airplane wings. The stated purpose was to heat the air between the wing coverings to prevent the formation of snow or ice thereon. The exhaust gases were then discharged to the atmosphere. b. British patent 137,082 to Tolputt, accepted January 8, 1920, suggested the delivery of engine exhaust gases into an airplane wing covered with aluminum alloy sheathing. The exhaust gases were led out of the interior of the wing through vents near the trailing edges of the wing. The specification mentioned silencing the exhaust and acknowledged that anti-icing had been previously proposed. Figures 1 and 2 of the British Tolputt patent are reproduced herewith. Hot exhaust gases from the engine Z pass through the main exhaust pipes Y to radiating manifolds E within the wing skin C'. The hot gases released through apertures E' in the manifolds E heat the skin C' and pass from the wing through vents C1. c. United States patent 1,650,665 to Thurston, filed May 16, 1921, disclosed a wing-type radiator for aircraft in which a portion of the wing was provided with a corrugated metal skin against a sheet metal plate. This construction provided a plurality of parallel water passages extending from a header in the leading edge to a return header in the trailing edge of the wing. Hot water from the engine water jackets was circulated through the water passages in the wing to cool the water. The exposed wing surface was heated, and such heating was incidental to cooling the engine coolant. d. United States patent 1,613,619 to Mummert, et al., filed November 29, 1922, disclosed a wing-type radiator similar to that disclosed by Thurston, but constructed in |