At last a way has been found to telephone across the Atlantic Ocean. That old scientific bugbear, the saturation of the cable covering with conflicting currents, which prevent the voice being heard over long distances, has been overcome, and nothing except the laying of a properly constructed cable now prevents our having direct speech with Europe.

The discovery is announced by Prof. M. I. Pupin of Columbia College, and even if Professor Pupin's reputation did not vouch for the authenticity of his claims, the enthusiastic manner of their acceptance by scientific men generally proves that a most important discovery has been made. Aside from this spectacular element of telephoning across the ocean, the discovery is of such value to land telephone and telegraph lines that not only will it be possible hereafter to talk directly between New York and San Francisco, but the cost of doing so can be reduced to what is now demanded for less than half that distance.

And yet this valuable discovery, although it required years of sifting through complicated forms to perfect it, is quite simple in character. It would remind you, as far as its quality of simplicity is concerned, of the mass of complicated designs which Edison adopted and discarded before he hit upon the simple vacuum bulb as a final form for the incandescent lamp.

Professor Pupin's invention consists of nothing more than series of simple coils of wire, to be inserted at intervals of eight to a mile under the sheath of the cable. This for the ocean telephone line.

For the land wire it will be necessary merely to connect the coils in circuit on telegraph poles at intervals of a mile apart. And these little coils, which you might almost make by twisting a single strand of wire around your finger, will bring the farthermost ends of the earth together in neighborly converse; will cheapen the cost of all telegraphic and telephonic communication.

What a wonder they were not thought of before?

They were, however, thought of many times and they were even tried. But, like many another revolutionary contrivance, they were discarded because the man who thought of them first had not the scientific acumen to apply them in the right manner.

This is where Professor Pupin came in. He knew of these trials and of the failures that resulted. He knew, in view of certain long observed phenomena in electrics, that the failures were unaccountable. Truly they should have been successes, not failures, by all laws. He sat him down to calculate it out mathematically, and finally, after several years of study, he evolved a theory that put him on the track of success.

Think of being occupied several years with a problem in mathematics. This is what Professor Pupin passed through. He also made some interesting experiments. Here, in short, is the problem that confronted him.

Most people suppose that electricity travels with the speed of light. The text-books say it does, and it is a favorite illustration with lecturers. But it is so only under certain conditions. There are other conditions, as in an Atlantic cable, for instance, where electricity takes quite an appreciable time to pass from one point to another.

If the man at the key on this side of the ocean presses down his instrument so as to send a signal across, there is no manifestation immediately at the other end. The current flows in and fills up not only the long wire, but also the gutta-percha covering, which has to become saturated with a certain amount before there is any current apparent at the other end. In other words, the cable may be likened to a bucket of water, and it must be filled completely before any current will run over. The same slow process must be gone through before the cable can be emptied and another signal sent through it. Hence the speed of cable transmission is a very limited number of words a minute. It is slow work. The trouble comes when you attempt to hurry the current, as in rapid telegraphing or in telephoning.

Every one knows that electricity travels in waves, and when you speak into a telephone receiver your voice sets the diaphragm going at a rate fast enough to send thousands of electric waves over the wire in a second. In other words, the wire is charged and discharged thousands of times a second. On comparatively short wires this is quite possible, but on long lines, and particularly on heavily insulated cable lines, these rapid pulsations would not become apparent at the other end except as a wild jumble. Since the cable refuses to allow any current to leak out of the other end until every part of it is slowly saturated, it is easy to see how the innumerable electric pulsations inspired by the voice would mingle and jumble and mix up indiscriminately in the cable and its covering, and how those which reached Europe, for instance, would have lost all specific character. The phenomenon is due, as electricians say, to the "capacity" of the cable.

Now it was also known to electricians that "capacity" could, under ordinary circumstances, be neutralized by what is known as a "choke coil." This is a simple coil of wire, which, when placed in circuit with any device which generated "capacity" (say a condenser), had the effect of rendering that capacity nil and allowing the current to flow on as before. Knowing this law and recognizing the cable as a sort of huge condenser, some one put a choke coil in circuit with the cable. The effect, however, was worse than before. The jumble was greater near the choke coil. No one could understand it.

The law had been laid down by Oliver Heaviside, the noted English physicist, and, as some one has said, the most eccentric scientist in the world, that capacity could be overcome by inductance. He did not say just how it was to be overcome, but he proved it mathematically. Ali of which may sound particularly odd to the layman not well versed in the higher mathematics. At any rate, here was the condition. According to the law we should have been able with certain apparatus to telephone across the ocean. Yet the apparatus did not accomplish the feat.

Professor Pupin thought the law might not have been interpreted aright, and he set out to study his theory. He also experimented. He caused to be set up in Columbia College an artificial telephone line 250 miles long, and he made all kinds of applications with choke coils to see if there might be some special way of applying them so as to attain the desired object. He also made another interesting experiment which any person may try and which illustrates very nicely how Professor Pupin's invention operates.

Recognizing a certain similarity in all wave motions, Professor Pupin fixed a tuning fork against the wall of the room, the prongs pointing outward horizontally. He tied a string to one of the prongs and then stretched it tightly across to the opposite wall of the room. When the fork was set vibrating, little waves passed over the strings to the wall and back. They were quite regular.

But he knew that, if the string had been continued on indefinitely for miles, the waves caused by the tuning fork would have thinned out and died away until finally, when a certain distance had been reached, there would be no wave motion perceptible. He took a little piece of beeswax and attached it to the string. The wave motion immediately showed much jumbling and irregularity. This, he thought, is exactly the condition of the Atlantic cable when one choke coil is placed on it. Then he fell to experimenting with the string and he attached pieces of beeswax to it at short intervals.

After a time he found that the waves sent away by the tuning fork passed in regular order over the string, being received, regulated, and passed along by the lumps of beeswax with remarkable dispatch. This, he thought, is what the cable needs—choke coils at intervals. The point was to determine the proper intervals. So he went back to his mathematics and to his artificial telephone line.

After a stupendous amount of work, Professor Pupin decided that on a submarine cable it would be necessary to insert eight coils to the mile in order that speech could be transmitted from New York to Europe. Whereas, on land telegraph lines, one coil to the mile would be quite sufficient. Of course, the laying of a submarine cable with eight coils to the mile attached at regular distances apart within the sheathing would be a prodigious commercial undertaking, but not nearly as much as was the laying of the first Atlantic cable.

The advantage to be gained, aside from the long-sought triumph of talking across the ocean, would be the immense quickening of all cable telegraphing.

The present rate of ocean telegraphing is five cycles a second. With the insertion of the coils it would be possible to operate at the rate of fifteen hundred cycles a second, or three hundred times as fast as is now possible. As Dr. Pupin points out, a cable three hundred times as fast as at present could do three hundred times as much business, and it could charge less than one-tenth of a cent a word for messages, and still earn as much money as at present.

So important do the telephone companies think Dr. Pupin's invention that they are already negotiating for its use.

With the use of the Pupin coil strung upon telegraph poles, one mile apart, it will be possible to telephone to San Francisco over thin iron wire, that will cost nothing comparatively in the building.

The use of the system on long land lines might even make a Pacific cable unnecessary, for the lines now connecting us with Alaska might be continued to Behring Strait and down again through Siberia to connect with Asia.

The New York Telephone Company placed its wires at the disposal of Dr. Pupin while he was making experiments.

Boston Herald.

Copyrighted, 1900, by Mary Baker G. Eddy.