volume 1, page 84.

ELECTRICAL SCIENCE: Development of the Telephone System.

The annual report of the American Telephone and Telegraph Company (by which the property and business of the American Bell Telephone Company were taken over at the close of the year 1899) for the year ending December 31, 1900, contains the following brief review of the development and growth of the telephone system, especially in the United States: "The year just passed rounds out the quarter century, within which is compassed the discovery and application of the art of transmitting speech by telephone. {441} A brief review of the development and growth of this new industry, which has become so important a factor in commercial and social life, seems appropriate at this time. Twenty-five years ago the wonderful invention of Professor Bell was made known to the world. Twenty-three years ago the first telephone exchange in the world was established in the United States, and from that beginning has been built up the great system of exchanges, and the network of connecting lines over which conversation can be held between points over a thousand miles apart. Twenty years ago there were 47,880 telephone subscribers in the United States, and 29,714 miles of wire in use for telephonic purposes. At the end of last year, there were 800,880 exchange stations equipped with our instruments, and 1,961,801 miles of wire were employed for exchange and toll line service. The United States has, from the beginning, held the leading place among nations in respect not only of the extensive development of the business, but in the employment of modern and improved appliances, tending to greater efficiency of service.

"In connection with the record of development of telephone service in this country, some comparison of the systems of foreign countries is of interest. The latest reports that can be obtained, part of which are for the year 1899, others to the close of 1900, show the countries next in order to the United States, as respects the development of telephone service, to be the German Empire, having 229,391 stations; Great Britain, 171,660; Sweden, 73,500; France, 59,927; Switzerland, 38,864: Austria, 32,255; Russia, 31,376; Norway, 29,446.

"As before stated, there were, at the close of last year, more than 800,000 stations connected with the exchanges of our licensee companies, which exceeds the aggregate number of subscribers in all the countries of Continental Europe. In addition to this, there were over 40,000 private line stations equipped with our telephones. The number of exchange and toll line connections in the United States now reaches almost two thousand millions yearly."

More detailed and precise statistics of the telephone service in the United States are given in the report as follows:

January 1, January 1, 1892. 1901.

Exchanges. 788 1,348 Branch offices. 509 1,427 Miles of wire on poles. 180,139 627,897 Miles of wire on buildings. 14,954 16,833 Miles of wire underground. 70,334 705,269 Miles of wire submarine. 1,029 4,203 Total miles of wire. 266,456 1,354,202 Total circuits. 186,462 508,262 Total employees. 8,376 32,837 Total stations. 216,017 800,880

The estimated number of exchange connections daily in the United States, made up from actual count in most of the exchanges, is 5,668,986. Or a total per year of about 1,825,000,000. The number of daily calls per station varies in different exchanges from 1 to 15.9, the average throughout the United States being 7.1. The average cost to the subscriber varies according to the size of the exchange and character of the service, from less than 1 to 9 cents per connection.

ELECTRICAL SCIENCE: Dr. Pupin's revolutionary improvement in long-distance Telephony.

The most important advance in telephonic science that has been made since the invention of the Bell instrument was announced at about the beginning of the new century, as the result of studies pursued by Dr. Michael I. Pupin, of Columbia University, New York. Mathematical and experimental investigations which Dr. Pupin had been carrying on, for several years, led him to a determination of the precise intervals at which, if inductance coils are inserted in a long conductor, an electric current in traversing it may be made to travel far without much loss of force. He is said to have taken a hint from seeing how waves of vibration in a cord are strengthened by lightly "loading" it at certain exact points, determined by the wave lengths. It is probably correct to describe his invention as being a scientific ascertainment of the points in a long telephonic circuit at which to load the electric current in it, and the precise loading to be applied.

In a paper published in the "Western Electrician," describing his investigations mathematically, Dr. Pupin wrote: "If an increase in efficiency of wave transmission over a cord thus loaded is to be obtained, it is evident that the load must be properly subdivided and the fractional parts of the total load must be placed at proper distances apart along the cord, otherwise the detrimental effects due to reflections resulting from the discontinuities thus introduced will more than neutralize the beneficial effects derived from the increased mass. … The insertion of inductance coils at periodically recurring points along the wave conductor produces the same effect upon electrical wave transmission as the distribution of the small loads along the stretched cord … produces upon mechanical wave transmission along the cord."

The result is said to be that conversation by telephone over a distance of 3,000 miles is made not only practicable but easy, and that it is believed to be as practicable through submarine cables as through overland wires. If it does not make the telephone a common instrument of communication from continent to continent, it will, at least, improve oceanic telegraphy beyond measure. According to newspaper report, Dr. Pupin's invention has been sold to the Bell Telephone Company for a very large sum.

ELECTRICAL SCIENCE: Wireless Telegraphy.

"In 1864 Maxwell observed that electricity and light have the same velocity, 186,400 miles a second, and he formulated the theory that electricity propagates itself in waves which differ from those of light only in being longer. This was proved to be true by Hertz, in 1888, who showed that where alternating currents of very high frequency were set up in an open circuit, the energy might be conveyed entirely away from the circuit into the surrounding space as electric waves. … He demonstrated that electric waves move with the speed of light, and that they can be reflected and refracted precisely as if they formed a visible beam. At a certain intensity of strain the air insulation broke down, and the air became a conductor. This phenomenon of passing quite suddenly from a non-conductive to a conductive state is … also to be noted when air or other gases are exposed to the X ray.

{442}

"Now for the effect of electric waves such as Hertz produced, when they impinge upon substances reduced to powder or filings. Conductors, such as the metals, are of inestimable service to the electrician; of equal value are non-conductors, such as glass and gutta-percha, as they strictly fence in an electric stream. A third and remarkable vista opens to experiment when it deals with substances which, in their normal state, are non-conductive, but which, agitated by an electric wave, instantly become conductive in a high degree. As long ago as 1866 Mr. S. A. Varley noticed that black lead, reduced to a loose dust, effectually intercepted a current from fifty Daniell cells, although the battery poles were very near each other. When he increased the electric tension fourfold to sixfold, the black-lead particles at once compacted themselves so as to form a bridge of excellent conductivity. On this principle he invented a lightning-protector for electrical instruments, the incoming flash causing a tiny heap of carbon dust to provide it with a path through which it could safely pass to the earth. Professor Temistocle Calzecchi Onesti of Fermo, in 1885, in an independent series of researches, discovered that a mass of powdered copper is a non-conductor until an electric wave beats upon it; then, in an instant, the mass resolves itself into a conductor almost as efficient as if it were a stout, unbroken wire. Professor Edouard Branly of Paris, in 1891, on this principle devised a coherer, which passed from resistance to invitation when subjected to an electric impulse from afar. He enhanced the value of his device by the vital discovery that the conductivity bestowed upon filings by electric discharges could be destroyed by simply shaking or tapping them apart. …

"The coherer, as improved by Marconi, is a glass tube about 1½ inches long and about 1/12 of an inch in internal diameter. The electrodes are inserted in this tube so as almost to touch; between them is about 1/30 of an inch filled with a pinch of the responsive mixture which forms the pivot of the whole contrivance. This mixture is 90 per cent. nickel filings, 10 per cent. hard silver filings, and a mere trace of mercury; the tube is exhausted of air to within 1/10000 part. … The coherer, when unexcited, forms a link which obstructs the flow of a current eager to leap across. The instant that an electric wave from the sending-station impinges upon the coherer it becomes conductive; the current instantly glides through it, and at the same time a current, by means of a relay, is sent through [a] powerful voltaic battery, so as to announce the signal through an ordinary telegraphic receiver.

"An electric impulse, almost too attenuated for computation, is here able to effect such a change in a pinch of dust that it becomes a free avenue instead of a barricade. Through that avenue a powerful blow from a local store of energy makes itself heard and felt. No device of the trigger class is comparable with this in delicacy. An instant after a signal has taken its way through the coherer a small hammer strikes the tiny tube, jarring Hs particles asunder, so that they resume their normal state of high resistance. We may well be astonished at the sensitiveness of the metallic filings to an electric wave originating many miles away, but let us remember how clearly the eye can see a bright lamp at the same distance as it sheds a sister beam. Thus far no substance has been discovered with a mechanical responsiveness to so feeble a ray of light; in the world of nature and art the coherer stands alone. …

"An essential feature of this method of etheric telegraphy, due to Marconi himself, is the suspension of a perpendicular wire at each terminus, its length twenty feet for stations a mile apart, forty feet for four miles, and so on, the telegraphic distance increasing as the square of the length of suspended wire. In the Kingstown regatta, July, 1898, Marconi sent from a yacht under full steam a report to the shore without the loss of a moment from start to finish. This feat was repeated during the protracted contest between the 'Columbia' and the 'Shamrock' yachts in New York Bay, October, 1899. On March 28, 1899, Marconi signals put Wimereux, two miles north of Boulogne, in communication with the South Foreland Lighthouse, thirty-two miles off. In August, 1899, during the manœuvres of the British navy, similar messages were sent as far as eighty miles. …

"A weak point in the first Marconi apparatus was that anybody within the working radius of the sending instrument could read its message. To modify this objection secret codes were at times employed, as in commerce and diplomacy. A complete deliverance from this difficulty is promised in attuning a transmitter and a receiver to the same note, so that one receiver, and no other, shall respond to a particular frequency of impulses. The experiments which indicate success in this vital particular have been conducted by Professor Lodge."

_G. Iles, Flame, Electricity and the Camera,