Telephone Lines and their Properties

Abstract

IN this book the author has attempted the difficult task of instructing both the student and the practical man, and the result is, on the whole, more successful than is usually the case. The first half of the book is a text-book of the modern practice of telephone lines in America, and contains a large amount of good and interesting information on overhead and underground lines, poles, insulators, wires, conduits, cables, exchanges, and switchboards. This covers too wide a field to be useful to a telephone engineer, as each subject is necessarily treated in a cursory manner, but to an English reader it is very interesting, if he knows enough of his own practice to note and appreciate the points of difference. Some of these indeed will make the general public thankful for the restrictions under which telephone men labour over here, and one of the illustrations—a street telephone pole, about 100 feet high, with eighteen heavy wooden -cross-arms—is a testimonial to the patience of American people. One or two of the explanations of facts outside strictly electrical information require revision; for instance, the coating formed on copper wire exposed to damp air is the hydrated carbonate of copper, and not the chloride, as stated by the author. Also the dictum on cables for underground circuits is somewhat curious, indiarubber insulation being condemned as not impervious to moisture, and liable to soften by heating, thereby allowing the wire to sink through the insulation. Considering that in another part of the book a current of ten milliamperes is given as a maximum for telephone work, it is difficult to see how any appreciable heating is to take place, as the current density is such as would rejoice the heart of Mr. Heaphy. Again, the accusation that indiarubber will not exclude moisture for a longer time than anything else, makes one wonder what they make it of in America. But after all these may be differences of opinion, and in general the information is unusually accurate, and is very clearly expressed. The only exception to this is in the chapter on switchboards, where the frequent use of technical terms is likely to give some difficulty to a student who is ignorant of practice. The addition of inverted commas to a technical expression is small assistance, where no explanation of its meaning is volunteered.

Telephone Lines and their Properties.

By William J. Hopkins. (London: Longmans, Green and Co.)