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decided: March 14, 1892.



Author: Brown

[ 144 U.S. Page 13]

 MR. JUSTICE BROWN delivered the opinion of the court.

The stress of this case is upon the question of patentable

[ 144 U.S. Page 14]

     novelty. The art of insulating electric wires has been known almost as long as that of conducting electricity for practical purposes by means of wires. Prior to the use of electricity for lighting, however, the feeble character of the currents conveyed upon these wires did not require that the insulating material should be non-combustible, and the skill of the inventor was directed toward a method of insulation which should protect the wire from moisture and other external injury. For this purpose the wires were covered with braid which had been saturated or covered with tar, paraffine, india-rubber, gutta-percha, asphaltum and various substances of like nature, to exclude the action of the water and afford a proper insulation.

Upon the introduction of electric lighting it was found that this method of insulation, while efficient to protect the wire from external influences, was unable to withstand the intense heat frequently generated in the wire itself by the powerful currents of electricity necessary for illuminating purposes. At first these wires were covered with cotton which had been saturated in paraffine and other similar substances; the result was that the insulating material was melted or set on fire, and dropped off the wire while still burning, and became so frequently the cause of conflagrations that the insurance companies declined to issue policies upon buildings in which this method of insulating wires was employed. A new substance was needed which would not only operate as a non-conductor of electricity, and as a protection against moisture, but which should also be non-combustible.

This material was discovered in ordinary paint. Mr. Cowles was not the first, however, to discover that paint was useful for the purpose of insulating electric wires. In several English patents put in evidence, paint is suggested as a proper covering for protective as well as for insulating purposes, in lieu of gutta-percha, india-rubber, resin, pitch or other similar substances, but as a non-combustible insulator was never required for telegraphing purposes, there is no intimation in any of them that it possessed this quality. It had, however, been a matter of common knowledge for many years that paint was

[ 144 U.S. Page 15]

     practically non-combustible. While the linseed oil in paint is to a certain extent combustible, the carbonate of lead is a material both non-combustible and a non-conductor.

It is clear that none of these English patents can be claimed as anticipations, since they all relate to the protection of land or submarine telegraph cables, and the use of paint, so far as it was used at all, was simply as a water-proof covering for a braided wire. There is nothing to indicate that the paint, as used by them, was applied in the manner indicated by the patent, or that it made the covering non-combustible, or was intended at all for that purpose.

The most satisfactory evidence of the use of a non-combustible covering for electric wires is found in the testimony of Edwin Holmes, manufacturer of an electric burglar alarm, who states that when he first commenced using electric conductors "the wire was insulated by winding a thread, larger or smaller as the case might be, around the wire, and that thread was covered with paint," and that all his wires were "insulated in that way until paraffine was substituted for the paint." The paint was applied by drawing the wire through a vessel containing the paint, and then through a piece of thick rubber or gutta-percha, which removed the surplus paint and left a smooth surface on the thread which covered the wire. He began to cover his wires in this way as early as 1860, and says that he accomplished his insulation "sometimes by covering the wire with a thicker thread and two coats or more of paint; sometimes by a thread covering and a coat of paint, then another thread covering and a coat of paint on that." And upon being asked to describe the condition of the first coating of paint when the second coating of fibrous material and paint was put on, he said: "The first coat was partially dried, so as to keep its place, but would admit of an impression from the next covering of thread." On being called upon subsequently for an affidavit to be used on an application for a rehearing, he stated that his object was not to produce a non-inflammable wire, and that the wire used by him was not non-combustible or non-inflammable, and was not better adapted for electric light conduction than the paraffine-coated wire. He

[ 144 U.S. Page 16]

     further stated that when the second layer of braid was laid on, the condition of the first layer was not such as to cause the threads of the second layer to force the paint into the interstices, and so load the wire with an abnormal quantity of paint, as is done in the process described in the Cowles patent. The substance of his testimony in this particular was, that the coating of paint upon his first layer was allowed to harden before the second layer was applied, so that the application of the second layer would ...

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