February 15, 1900] 



NA TURE 



377 



must, therefore, be of the very highest order. His scientific 

 training and his world-wide practice have broadened his views 

 and enlarged his mind. Above all, his character must be above 

 all reproach. The honour of the engineer is the honour of his 

 j)rofession. The Lord Chief Justice's Bill was welcomed by 

 every member of the Institution of Civil Engineers. The evil 

 it is desired to suppress is very great and very wide, but it is 

 not the characteristic of the engineer. 



Let me, in conclusion, impress on you the antiquity and the 

 universality of the functions of the engineer. Tul)al-Cain was 

 an instructor of every artificer in brass and iron, and this before 

 the flood. The very earliest remains of Egyptian, Babylonian 

 and Assyrian temples and monuments indicate a wonderful 

 knowledge of the strength of materials. The Cloaca Maxima 

 of the early Latin King Tarquinius Priscus exists still, though 

 built 2,600 years ago. In the track of war and diplomacy, in 

 the earliest days of history, went trade and commerce. The 

 general became the engineer. Western Asia was covered with 

 roads, not only to facilitate the transport of troops and chariots, 

 but to assist the merchant in the distribution of his wares. In- 

 tercourse of all kinds has always been the outcome of civilisa- 

 tion. The balance of power falls to the strong. In days of old 

 it was to the strong physically. In modern days it is more to 

 the strong mentally and financially. The greatest political gift 

 that mind can give to man, the greatest security for peace and 

 comfort, is the ability to wield the great powers of nature so as 

 to destroy human life with the greatest rapidity and at the 

 greatest distance. An overpowering fleet and an efficient army 

 are our insurance for security at home. There is not a habit- 

 able spot on the face of the earth that does not bear traces of 

 the presence of the engineer. He is the great civiliser. He 

 not only immediately follows, but he sometimes even precedes 

 the military conqueror. He distributes peace and good-will 

 without the accompaniments of fire, blood and famine. Mr. 

 Cecil Rhodes is opening up Africa with the " wonder-working 

 wire." Khartoum has been brought within seventy hours of 

 Cairo by train, and ere long, when peace is restored in that 

 self-disturbed country, South Africa, Cairo and Cape Town will 

 I)e in direct and immediate communication by telegraph, and 

 eventually by rail. 



The engineer is not only a benefactor to his race, but he is a 

 necessity of the age. 



WIRELESS TELEGRAPHY} 

 "^V'HEN Ampere threw out the suggestion that the theory of a 

 universal ether, possessed of merely mechanical properties, 

 might supply the means for explaining electrical facts, which 

 view was upheld by Joseph Henry and Faraday, the veil of 

 mystery which had enveloped electricity began to lift. When 

 Maxwell published, in 1864, his splendid dynamical theory of 

 the electro-magnetic field, and worked out mathematically the 

 theory of ether waves, and Hertz had proved experimentally 

 the correctness of Maxwell's hypothesis, we obtained, if I may 

 use the words of Prof. Fleming, "the greatest insight into the 

 hidden mechanisms of nature which has yet been made by the 

 intellect of man." 



A century of progress such as this has made wireless tele- 

 ^^raphy possible. Its basic principles are established in the very 

 nature of electricity itself. Its evolution has placed another 

 great force of nature at our disposal. 



We cannot pay too high a tribute to the genius of Heinrich 

 Hertz, who worked patiently and persistently in a new field of 

 experimental physics, and made what has been called the 

 greatest discovery in electrical science in the latter half of the 

 nineteenth century. He not only brought about a great 

 triumph in the field of theoretical physics, but, by proving 

 Maxwell's mathematical hypothesis, he accomplished a great 

 triumph in the progress of our knowledge of physical agents and 

 physical laws. 



I cannot forbear saying one word as to the eminent electri- 

 cian who was placed in his last home as recently as Saturday 

 last, for it is manifest that several years ago Prof. Hughes was 

 on the verge of a great discovery, and, if he had persevered in his 

 experiments, it seems probable that his name would have tieen 

 closely connected with wireless telegraphy as it is with so many 

 branches of electrical work in which he gained so much renown 

 and such great distinction. 



at the Royal Institution, on 



1 Abridged from a discourse delivered 

 ebruary 2, by Mr. G. Marconi. 



NO. I581, VOL. 61] 



The experimental proof by Hertz thirteen years ago, of the 

 identity of light and electricity, and the knowledge of how to 

 produce, and how to detect these ether waves, the existence of 

 which had been so far unknown, made possible true wireless 

 telegraphy. I think I may be justified in saying that for 

 several years the full importance of the discovery of Hertz was 

 realised but by very few, and for this reason the early de- 

 velopment of its practical application was slow. 



The practical application of wireless telegraphy at \\it present 

 time is many times as great as the predictions of five years ago 

 led us to expect in so short a time. The development of the 

 art during the past three or four years, and its present state of 

 progress, may perhaps justify the interest which is now taken 

 in the subject. Yet only a beginning has been made, and the 

 possibilities of the future can as yet be only incompletely 

 appreciated. All of you know that the idea of communicating 

 intelligence without visible means of connection is almost as 

 old as mankind. Wireless telegraphy by means of Hertzian 

 waves is, however, very young. I hope that if I pass over the 

 story of the growth of this new art, as I have watched it, or do 

 not attempt to prove questions of priority, no one will take it 

 for granted that nothing is to be said on these subjects, or that 

 all that hai been said is entirely correct. 



The time allowed for this discourse is too short to permit me 

 to recount all the steps that have led up to the practical 

 applications of to-day. I believe it will probably interest you 

 more to hear of the problems which have lately been solved, 

 and the very interesting developments which have taken place 

 during the last few months. 



I find that a great element of the success of wireless tele- 

 graphy is dependent upon the use of a coherer such as I have 

 adopted. It has been my experience, and that of other workers, 

 that a coherer as previously constructed — that is, a tube several 

 inches long partially filled with filings enclosed by corks — was 

 far too untrustworthy to fulfil its purpose. I found, however, 

 that if specially prepared filings were confined in a very small gap 

 (about I mm.) between flat plugs of silver, the coherer, if pro- 

 perly constructed, became absolutely trustworthy. In its normal 

 condition the resistance of a good coherer is infinite, but when 

 influenced by electric waves the coherer instantly becomes a 

 conductor, its resistance falling to 100 or 500 ohms. This con- 

 ductivity is maintained until the tube is shaken or tapped. 



I noticed that by employing similar vertical and insulated 

 rods at both stations it was impossible to detect the effects of 

 electric waves of high frequency, and in that way convey the 

 intelligible alphabetical signals, over distances far greater than 

 had been believed to be possible a few years ago. 



I had formerly ascertained (see paper read before the Institu- 

 tion of Electrical Engineers by G. Marconi, March 1899) that the 

 distance over which it is possible to signal with a given amount 

 of energy varies approximately with the square of the height of 

 the vertical wire, and with the square root of the capacity of a 

 plate, drum, or other form of capacity area which may be placed 

 at the top of the wires. 



The law governing the relation of height and distance has 

 already been proved correct up to a distance of 85 miles. Many 

 months ago it was found possible to communicate from the 

 North Haven, Poole, to Alum Bay, Isle of Wight, with a height 

 of 75 feet, the distance being 18 miles. Later on two instal- 

 lations with vertical wires of double that length, i.e. 150 feet, 

 were erected at a distance of 85 miles apart, and signals were 

 easily obtained between them. According to a rigorous appli- 

 cation of the law, 72 miles ought to have been obtained instead 

 of 85 ; but, as I have previously stated, the law has been proved 

 only to be approximately correct, the tendency being always on 

 what I might call the right side ; thus we obtain a greater dis- 

 tance than the application of the law would lead us to believe. 

 There is a remarkable circumstance to be noted in the case of 

 the 85 miles signalling. At the Alum Bay station the mast is 

 on the cliff, and there is no curvature of the earth intervening 

 ^tween the two stations ; that is to say, a straight line between 

 the base of the Haven and Alum Bay stations would clear the 

 surface of the sea. But in the case of the 85 miles the two 

 stations were located on the sea-level, and between them exists 

 a hill of water, owing to the earth's curvature, amounting to 

 over 1000 feet. If these waves travelled only in straight lines, 

 or the effect was noticeable only across open space, in a direct 

 line, the signals would not have been received, except with a 

 vertical wire 1000 feet high at both stations. 



While carrying out some experiments nearly three years ago 



