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Prof. Adams announces, and with truth, that street railways have never before been brought within the scope of the census statistics of transportation, and he points out the peculiar difficulties which were met with in collecting the facts already presented. As business is extended, and the room and area formerly occupied by people are taken for great mercantile houses and for manufacturing, the population of such areas is sent out to the suburbs of necessity, while many seek suburban residences as a matter of choice. From my knowledge of some of the men who have been foremost in projecting lines of rapid transit, but who have been accused of doing it for entirely selfish motives, I learn that public benevolence has influenced them to a sufficient extent to induce them to take the great risks which are apparently involved. I believe, therefore, that all the efforts that are being made to secure convenient and cheap rapid transit in great cities are those which should bring to their support the help of all men who are seeking the improvement of the condition of the masses.

The special experts have selected cities on a basis of an estimate of population made at the time the compilation of the tables was begun. Suburban lines tributary to large cities, but without their corporate limits, as well as those actually within the cities, are included in the statement; as, for instance, where cities situated close together have a common street-railway system, it has not been thought best by the experts to attempt a separation in the tables. The street-railway lines comprehended in Boston traverse also Lynn, Cambridge, and other suburban places. Another type of electric power cable is installed in underground ducts and is extensively used in cities where lack of space or considerations of safety preclude the use of overhead lines. The number and type of protective layers surrounding the core depends upon the use for which the cable is intended. A coaxial cable, which first gained widespread use during World War II, is a two-conductor cable in which one of the conductors takes the form of a tube while the other (smaller but also circular in cross section) is supported, with a minimum of solid insulation, at the centre of the tube.

Unlike an aerial cable, a buried cable invariably uses commercially pure copper or aluminum (mechanical strength is not a problem underground), and the stranded conductor is frequently rolled to maximize its compactness and electrical conductance. In general, the core is covered with a layer of copper to improve conduction over long distances, followed by a material (e.g., aluminum foil) to block the passage of water into the fibres. They usually consist of an aluminum or lead-alloy tube or of a combination of metallic strips and thermoplastic materials. The cable core contains a single solid or stranded central strength element that is surrounded by optical fibres; these are either arranged loosely in a rigid core tube or packed tightly into a cushioned, flexible outer jacket. The insulation of a telephone cable is composed of dry cellulose (in the form of paper tape wrapped around the conductor or paper pulp applied to the conductor) or of polyethylene.

The construction of long submarine cables for either telephone or telegraph service is somewhat different from that discussed previously. Such cables usually consist of a core embedded in a series of protective layers. It has been urged that an iron-covered cable, suspended from one point to another, gradually becomes weaker, that rust and marine growth or deposit accumulate and break the cable with their weight; but I do not know of any instance in support of the assumption, nor is it at all certain that a simple unprotected core would exist for any length of time, or be in any way better adapted for the supposed conditions. In a fibre-optic cable, light signals are transmitted through thin fibres of plastic or glass from light-emitting diodes or semiconductor lasers by means of internal reflection. Cables made of optical fibres first came into operation in the mid-1970s. On December 31, 1889, 476 cities and towns in the United States possessed rapid transit facilities, the total number of railways in independent operation being 807. Many railroads, however (and the number is stated at 286, having a total length of 3,150·93 miles, and 13, having a total length of 135·75 miles), have as yet made no report; while in six the returns received were so imperfect that it was necessary to supplement them by approximations.

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