Certiorari was granted, 290 U.S. 624, 54 S.Ct. 372, 78 L.Ed. -, to review a decree of the Court of Appeals for the Second Circuit, affirming a decree of a District Court holding invalid, for want of invention, the Torchio patent, No. 1,172,322, of February 23, 1916, applied for March 15, 1915, for 'an improvement in protective devices for electric cable joints.' 66 F.(2d) 739. The Court of Appeals for the Sixth Circuit had previously held the patent valid and infringed. Metropolitan Device Corp. v. Cleveland Electric Illuminating Co., 36 F.(2d) 477.
Correct appreciation of the contentions made requires at the outset some discussion of the structure of electric cables for the transmission of high-tension (voltage) electric currents and, more particularly, the causes of leakage or wastage of current at the joints of such cables, for the prevention of which the patented device is said to be useful. Cables for the transmission of high-tension currents comprise a plurality of copper conductors, usually three in number, each covered with an insulating tape of paper or fabric, inclosed in an outer insulating wrapping, and all in turn surrounded by pervious insulating material filling the interstices between the conductors and saturated with oil. The whole is inclosed in a lead tube or sheath, which constitutes the outer surface or cover of the cable. In practice, the cables are spliced or connected by forming a joint at the connecting ends. This is accomplished by cutting back the lead sheath for a suitable distance, bringing the ends of the conductors together and joining them, usually by a connecting copper sleeve, and covering or surrounding them with successive wrappings or layers of insulating material, impregnated with an insulating compound such as an oil, long recognized as a desirable insulating material. A cylindrical lead sleeve is then placed over the joint and soldered at its ends to the lead sheath of the cable so as to surround and hermetically inclose the joint. Through openings made in the sleeve insulating compounds may be introduced.
Leakage of current at the joint results from imperfect insulation. Deterioration in the insulation may result from the drying out of the insulating material, particularly through loss or 'bleeding' of the insulating fluid at the ends, or when the cable is cut. Also high-tension currents, ranging upwards from 15,000 volts, develop heat in the conductors and adjacent material, with consequent expansion and corresponding contraction when cooling, known as 'breathing.' This causes migration of the in sulating compound within the cable and to some extent its extrusion, and produces cracks and voids in it, with resulting ionization of the interstitial air at high tensions, and the lowering of the dielectric strength or resistance of the cable at the joint.
The patent claimed is for a device, in combination, to prevent current leakage by improving the insulation. Claim 4, upon which alone the petitioner relies, reads:
'4. An electric cable, comprising a sheath, a line conductor having a joint, a body of pervious insulating material inclosing said joint, the said sheath being removed for a distance sufficient to expose said pervious body, a sleeve of impervious material of greater diameter than said body, inclosing the same and hermetically united at its ends to said cable sheath, a receptacle communicating with the interior of said sleeve, and an insulating fluid adapted to permeate said pervious body contained in said receptacle and the space between said body and said sleeve.'
On February 11, 1927, before either the present suit or that in the Sixth Circuit was begun, an assignee of the patent and petitioner's predecessor in interest filed a disclaimer of the improvement, 'except for electric cables which comprise a line conductor, insulating wrapping permeated with insulating compound and a sheath of flexible, inelastic metal constituting a unitary product of manufacture and commerce which is portable and capable of being drawn through conduits; and except as to an insulating liquid which is fluid at ordinary working temperatures of such cables and in quantity sufficient to supply at all times the demands made by the cable in use, and by the joint.'