After his December, 1901 announcement that he had successfully transmitted radio signals from England to Newfoundland, Guglielmo Marconi was disappointed to find skepticism over whether he had sufficiently substantiated his historic claim. In order to counter these lingering doubts, in February, 1902 he conducted a series of carefully documented tests aboard the S.S. Philadelphia, on a voyage westward across the Atlantic from France. During this trip Marconi kept detailed records -- his challenge at the end of the voyage of "Can you read? Will they say now I was mistaken in Newfoundland?" was an unusually strong statement by the usually reserved inventor.
The test results included coherer-tape reception up to 1,551 miles (2,496 kilometers), and audio reception up to 2,099 miles (3,378 kilometers). However, there was one significant difference compared to the Newfoundland tests -- the maximum distances had occurred at night. Although not mentioned in the article, the maximum daytime reception aboard the S.S. Philadelphia had only been about 700 miles (1,125 kilometers), less than half of the distance which had been claimed in the Newfoundland tests, which had also taken place during daylight hours. Still, the S.S. Philadelphia tests did conclusively prove that radio signals were now being transmitted hundreds of kilometers farther than previously had been possible.
The S.S. Philadelphia tests were the first to show that long-distance reception generally was better at night than during the day, something which came as a complete surprise to Marconi. At first he thought there might be some sort of effect of sunshine on the receiving antenna -- eventually it was determined that a change in the ionosphere causes it to reflect radio waves back to earth during darkness.
McClure's Magazine, April, 1902, pages 525-527:
MESSAGES TO MID-OCEAN.
MARCONI'S OWN STORY OF HIS LATEST TRIUMPH.
RECORDED BY HENRY HERBERT MCCLURE.
EVER since Marconi announced that he had received telegraph signals from Cornwall, England, at St. John's, Newfoundland, there has been a growing doubt in many minds as to whether he had really accomplished the feat. Marconi has settled all those doubts now. On board the "Philadelphia," during the week of February 22d, a receiver took and printed on a tape messages from Cornwall, 1,551 miles away. Notice this statement. No telephone instrument was used; there was no human agency to "think" or "imagine," and perhaps err. At a prearranged hour a transmitter at Cornwall shot a message through the air; Marconi and the ship's officers and others on board the "Philadelphia" heard the tick, and, looking at the tape, saw the dots and dashes which you or I or anybody still can see. When a machine does a thing, we humans believe; so long as a man stands between, we doubt.
Fully two miles of telegraph tape, covered with thousands of signals and messages, bear witness to this latest triumph. By way of voucher, the captain and chief officer of the "Philadelphia" signed and certified the messages and signals which they saw printed by the instruments, and the documents in the case thus presented include messages received up to 1,551.5 miles, and signals received up to 2,099 miles. All this happened on a ship which was steaming away from England at twenty knots an hour; and under conditions which permit no question as to the significance of the experiments.
"Can you read?" inquired Marconi of the writer of this article the day he arrived fresh from his triumph and full of enthusiasm. "Will they say now I was mistaken in Newfoundland?" and he pointed to a piece of tape, the full length of which was covered with the blue marks of a telegraphic inker. It bore the inscription, "Received on S.S. 'Philadelphia,' Lat. 42.1 N., Long. 47.23 W., distance 2,099 (two thousand and ninety-nine) statute miles from Poldhu. Capt. A. R. Mills."
"Before I sailed from England," said Mr. Marconi, "I gave instructions to the operators at my Poldhu station to the effect that they should send signals at stated intervals during the week of my voyage. They were to operate two hours out of every twelve, or one hour out of every six, sending messages and signals in periods of ten minutes, alternating with intervals of five-minute rests."
Marconi's party occupied four staterooms on the upper deck. On a small table in one of these the instruments rested. It was the same installation as is used on all the transatlantic steamers equipped with his apparatus, except that this one was fitted with special coherer attachments which attuned it to the Poldhu station. Outside of the cabin there was little to be seen. One wire passed through a porthole of the operating-room and was fastened to the side of the ship, thus establishing a "ground"; and in place of one aërial wire extending to the top of the ship's mast, four were used in parallel, in order that a better effect might be secured. The end of these four wires was 150 feet above the water-line, a fact worthy of note in comparison with the height of the kites and balloon at St. John's--over 400 feet.
At Poldhu, the sending station, there was used practically the same apparatus as for the Newfoundland experiments. Engines and dynamos generating from six to forty horsepower of energy created a voltage of 20,000, and this high tension was transformed up to 250,000. When the operator pressed the telegraphic key, a spark a foot long and as thick as a man's wrist, the most powerful electric flash yet devised, sprang across the gap; the very ground near by quivered and crackled with the energy. No human being could stand near the huge coil which produced this tremendous flash of lightning. Of so great a power must be the transatlantic stations, in order that 3,000 miles away a few slender wires may pick up an infinitesimally small part of the energy radiated, and the receiving instruments record the message that speeds like light across the space. With every tick of the inker on the tape there are hundreds of thousands of waves in the ether to produce it; with every flash of the transmitting instruments, hundreds of thousands of ether waves have circled the globe in all directions. Yet, thanks to this young man of twenty-seven years, the proper message is received by the proper station; and, to the world, what was hardly a probability three months ago is now an undisputed fact.
The "Philadelphia" left Cherbourg at midnight, February 22d. Several messages were sent and received until the 150 mile limit was passed. About six P.M. on the 23d, when the liner was 250 miles out, there came the message:
"Stiff southwest breeze; fairly heavy swell."
And on the next morning, at the appointed time:
"All in order. V. E. (Do you understand?)"
Chief Officer Marsden happened to be in the operating-room when this message was ticked out. The ship was then 500 miles away from Poldhu, and he could scarcely credit his senses. He had actually seen it, and, full of excitement, he rushed about the ship, telling his fellow-officers of the feat.
"Ho, ho!" they laughed. "Do you think we are going to believe that?"
"Wait until the set time to-morrow, then, and see for yourselves," replied Marsden.
The next day the skeptics crowded about the operating-room. Watch in hand, Marconi sat looking at his instruments. Then he opened a brake on the coil of tape, and the white strip began to unroll. Suddenly Marconi burst out, "There it comes," and simultaneously began the "tap, tap, tap" of the inker, and another message had waved itself through the ether, and had been recorded on a piece of narrow paper nearly 1,000 miles away from its source.
The days following were full of suppressed excitement. Shortly after midnight on the 24th, amidst scores of signals, came the message:
The distance was then 1,032.3 miles. Another about the same time read:
"Thanks for telegram. Hope all are still well. Good luck."
The supreme test for messages came when the ship was 1,551.5 miles from Poldhu.
At that time, just before the break of day, on the 25th came the message:
"All in order. Do you understand?"
"Let me show you just how accurately these instruments operate," said Marconi to Captain Mills. (The ship was then in mid-ocean.) "I will release the brake on the coil of tape just a few seconds before the appointed time, and we shall see when the signals begin, and whether they come as they should."
Mr. Marconi and the captain held their watches. Ten seconds before the expected working period a snap of the brake set the coil in motion. The two waited with breathless expectancy. The captain had been one of the skeptics at the start. Now he was all confidence and enthusiasm. Almost exactly on the second for which they were waiting there was a slight buzz near the coherer. Marconi lifted his hand. "Tap, tap, tap," sounded the inker as it clicked against the tape. The young man smiled. "Is that proof enough, Captain?" For exactly ten minutes the signals continued in unbroken order.
"Now," said Marconi,"let us see whether these instruments will get anything during the five minutes' rest period of the Poldhu operators. You know some of the scientists say my receivers may be affected by atmospheric electricity. It is possible, too, that some of the other ocean liners equipped with my system may be operating within range of this ship. If they are, we shall not know it, for these instruments are tuned to receive messages from the Cornwall station only. But some people say I cannot tune my messages."
Again the two waited beside the instruments. Nothing appeared on the tape, although it was allowed to unroll during the time. Then again, as suddenly and as strangely as before, began the "tap, tap, tap" of the inker. The Poldhu operators had returned to their labors, and Marconi, half way across the ocean, was getting the click every time they pressed the key and sent that enormous flash of energy across the sparkling gap of the transmitter.
The signals continued to come during the Working periods of the next day. Shortly before the end of the appointed hour in the evening, the last set of signals arrived. The ship was 2,099 miles from Poldhu. The record established at Newfoundland had been broken, and the proof of Marconi's achievement was indisputable.
No one could doubt that the signals had been received, and the fact that the steamship "Umbria," which was equipped with a Marconi installation, and only a few hours behind the "Philadelphia," did not receive a single signal from Poldhu proves conclusively Marconi's assertion that he can so regulate his instruments that only the proper stations shall receive certain messages.
"I knew the signals would come up to 2,100 miles, because I had fitted the instruments to work to that distance," he replied to a question. "If they had not come, I should have known that my operators at Poldhu were not doing their duty.
"Why, I can sit down now and figure out just how much power, and what equipment would be required to send messages from Cornwall to the Cape of Good Hope or to Australia. I cannot understand why the scientists do not see this thing as I do. It is perfectly simple, and depends merely on the height of wire used and the amount of power at the transmitting ends. Supposing you wanted to light a circuit of 1,000 electric lamps. You would use enough dynamos and produce enough current for that effect. If you did not have that much power, you could not operate 1,000 lamps. It is the same with my system. We found several years ago that, if we doubled the height of our aërial wire, we quadrupled the effect. We used one-fortieth of a horse-power then. Now I use several horsepower, and, by producing a powerful voltage, I naturally get an effect in proportion to that power. It is not possible to keep on extending the height of our aërial conductors, so we simply use more power when we wish to do long distance work.
"Give me a week at Nantucket and I will guarantee to receive signals from England. As soon as we can get up stations in this country similar to our station at Poldhu we shall be able to transmit and receive any and all kinds of messages across the Atlantic."
It is the first prophecy that Marconi has made since he began his work in wireless telegraphy seven years ago. He has not failed before. Few believe that he will fail now.