File:Bell telephone magazine (1922) (14569509009).jpg

Identifier: belltvol20elephonemag00amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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made practicableseveral major advances in manufac-turing technique, and these have re-duced the cost and improved the uni-formity of the product. 1 HE most vital part of the relay,and at the same time one of the mostvulnerable, is the tiny projecting con- tact welded to the contact spring.The shape of this contact and themetal of which it is made are of greatimportance in determining the relaysreliability, and have been the subjectof almost continuous laboratory study.Extensive investigations have beenmade of the behavior of contacts ofvarious metals and shapes when sub-jected to mechanical action and toerosion of an electric spark, theamount and effect of tarnish, the pres-sure required for good contact, andthe effect of foreign particles. Silver, tungsten, platinum, rhodium,iridium, gold, and palladium, and theiralloys, all find use as relay contacts.Years of experience have shown thatprecious metals are better than basemetals for contact purposes. For 19^ 1 Evolution by Design 145
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Components oy Cables Ai the top is shown one of the two coaxial conductors pictured in the cable at the right on theopposite page. The central wire is held in place by insulating discs and enclosed in a coppertube which is wound about by two steel tapes, and is enclosed, with its twin and two sets ofquads, in a lead sheath. Below is a quad, composed of four copper wires, each wrappedin paper insulation and then twisted together. Coaxial cable is cheaper per mile to makethan the quadded cable shown opposite, but requires more expensive terminal equipment many kinds of relay, silver or pal-ladium is the most satisfactory. Asregards shape, the older contact, withits pin-head contour, has been re-placed by one in the form of a tinybar about one-sixteenth inch long andone-sixtyfourth inch high. The barof one spring is mounted horizontallyand the bar of its companion springvertically, so that the two contacts,when touching each other, are in theform of a cross. r OREIGN particles have been

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