i64 



NA TURE 



[June i 7, 1897 



The Tratismitter. — His transmitter is Prof. Righi's iorm of 

 Hertz's radiator. 



Two spheres of solid brass, 4 inches in diameter, are fixed in an 

 oil-tight case of insulating material, so that a hemisphere of 

 each is exposed, the other hemisphere being immersed in a bath 

 of vaseline oil. The use of oil has several advantages. It 

 maintains the surfaces of the spheres electrically clean, avoiding 

 the frequent polishing required by Hertz's exposed balls. It 

 impresses on the waves excited by these spheres a uniform and 

 constant form. It tends to reduce the wave-lengths— Righi's 

 waves are measured in centimetres, while Hertz's were measured 

 in metres. For these reasons the distance at which effects are 

 produced is increased. Mr. Marconi uses generally waves of 

 about 120 centimetres long. Two small spheres are fixed close 

 to the large spheres and connected each to one end of the 

 secondary circuit of the " induction coil," the primary circuit of 

 which is excited by a battery, thrown in and out of circuit by 

 the Morse key. Now, whenever the key is depressed sparks 

 pass between the small and large spheres, and since the system 

 formed by the large spheres contains capacity and electric 

 inertia, oscillations are set up in it of extreme rapidity. The fre- 

 quency of oscillation is probably about 250 millions per second. 



The distance at which effects are produced with such rapid 

 oscillations depends chiefly on the energy in the discharge that 

 passes. A 6-inch spark coil has sufficed through the system of 

 spheres up to four miles, but for greater distances we have used 

 z. more powerful coil — one emitting sparks 20 inches long. It may 

 also be pointed out that this distance increases with the diameter 

 of the large spheres, and it is nearly doubled by making the 

 spheres solid instead of, hollow. 



The Receiver. — Marconi's relay consists of a small glass tube 

 four centimetres long, into which two silver pole-pieces are 

 •tightly fitted, separated from each other by about half a milli- 

 metre — a thin space which is filled up by a mixture of fine 

 nickel and silver filings, mixed with a trace of mercury. The 

 tube is exhausted to a vacuum of 4 mm., and sealed. It forms 

 part of a circuit containing a local cell and a sensitive telegraph 

 relay. In its normal condition the metallic powder is virtually 

 an insulator. The particles lie higgledy-piggledy, anyhow in 

 ■ disorder. They lightly touch each other in an irregular method, 

 but when electric waves fall upon them, they are " polarised," 

 order is installed. They are marshalled in serried ranks, they 

 are subject to pressure — in fact, as Prof. Oliver Lodge expresses 

 it, they "cohere" — electrical contact ensues, and a current 

 passes. The electric resistance of Marconi's relay — that is, the 

 resistance of the thin disc of loose powder — is practically infinite 

 when it is in its normal or disordered condition. It is then, in 

 (fact, an insulator. This resistance drops sometimes to five 

 ■ohms, when the absorption of the electric waves by it is intense 

 it therefore becomes a conductor. It may be that we have in 

 the measurement of the variable resistance of this instrument a 

 means of determining the intensity of the energy falling upon it. 

 This variation is being investigated both as regards the magni- 

 tude of the energy and the frequency of the incident waves. 

 Now such electrical effects are well known. In 1866 Mr. S. A. 

 Varley introduced a lightning protector constructed like the 

 tube, but made of boxwood and containing powdered carbon. 

 It was fixed as a shunt to the instrument to be protected. It 

 acted well, but it was subject to this coherence, which rendered 

 the cure more troublesome than the disease, and its use had to 

 be abandoned. The same action is very common in granulated 

 carbon microphones like Hunning's, and shaking has to be re- 

 sorted to to decohere the carbon particles to their normal state. 

 M. E. Branly (1890) showed that copper, aluminium and iron 

 filings behaved in the same way. Prof. Oliver Lodge, who has 

 done more than any one else in England to illustrate and 

 popularise the work of Hertz and his followers, has given the 

 name " coherer" to this form of apparatus. He has much im- 

 proved it. Marconi "decoheres" by making the local current 

 very rapidly vibrate a small hammer-head against the glass tube, 

 which it does effectually, and in doing so makes such a sound 

 that reading Morse characters is easy. The same current that 

 decoheres can also record Morse .signals on paper by ink. The 

 exhausted tube has two wings which, by their size, tune the re- 

 ceiver to the transmitter. Choking coils prevent the energy 

 escaping. Oscillations set up in the transmitter fall upon the 

 receiver tuned in sympathy with it, coherence follows, currents 

 are excited, and signals made. 



In open clear spaces within sight of each other nothing more 

 is wanted, but when obstacles intervene and great distances are 



NO. 1442, VOL. 56] 



in question height is needed ; tall masts, kites, and balloons have 

 been used. Excellent signals have been transmitted between 

 Penarth and Brean Down, near Weston-super-Mare, across the 

 Bristol Channel, a distance of nearly nine miles. 



It is curious that hills and apparent obstructions fail to 

 obstruct. The reason is probably the fact that the lines of force 

 escape these hills. Weather seems to have no influence ; rain, 

 fogs, snow and wind, avail nothing. 



There are some apparent anomalies that have developed 

 themselves during the experiments. Mr. Marconi finds that his 

 relay acts even when it is placed in a perfectly closed metallic 

 box. This is the fact that has given rise to the rumour that he 

 can blow up an ironclad ship. This might be true if he could 

 plant his properly tuned receiver in the magazine of an enemy's 

 ship. Many other funny things could be done if this were 

 possible. I remember in my childhood that Captain Warner 

 blew up a ship at a great distance off Brighton. How this was 

 done was never known, for his secret died shortly afterwards 

 with him. It certainly was not by means of Marconi's relay. 



The distance to which signals have been sent is remarkable. 

 On Salisbury Plain Mr. Marconi covered a distance of four 

 miles. In the Bristol Channel this has been extended to over 

 eight miles, and we have by no means reached the limit. 



It is easy to transmit many messages in any direction at the 

 same time. It is only necessary to tune the transmitters and 

 receivers to the same frequency or "note." Enough has been 

 done to prove its value, and to show that for shipping and 

 lighthouse purposes it will be a great and valuable acquisition. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Oxford.— Mr. R. A. Buddicom, Scholar of Keble College, 

 has been elected to the University Biological Scholarship at 

 Naples. 



The University, in view of the visit of so many distinguished 

 men to England for the Diamond Jubilee celebrations, has decided 

 to confer the honorary degree of D.C. L. on Her Majesty's 

 Premiers, amongst others, at this year's Commemoration. The 

 following will therefore be the recipients of this honour : — The 

 Hon. W. Laurier, Premier of the Dominion of Canada ; Hon. 

 Sir W. V. Whiteway, K.C.M.G., Premier of Newfoundland ; 

 Hon. Sir J. Gordon Sprigg, K.C.M.G., Premier of Cape 

 Colony ; Hon. G. H. Reid, Premier of New South Wales ; 

 Hon. G. C. Kingston, Premier of South Australia ; Hon. Sir 

 H. M. Nelson, K.C.M.G., Premier of Queensland; Hon. G. 

 D. Taubman-Goldie, K.C. M.G. , Governor of the Royal Niger 

 Company ; and Mr. E. H. Godkin, of New York. 



The Junior Scientific Club met on June 9 and 16. Papers 

 were read by Mr. R. R. Marett (Exeter), on the sanctions 

 of savage morality ; and by Messrs. P. Elford (St. John's) 

 and N. E. Moss (Trinity) on artificial silks ; E. H. Hunt 

 (Balliol) and A. S. Fisher (New College). 



Convocation on Tuesday unanimously passed a decree con- 

 veying the cordial thanks of the University to the Worshipful 

 Company of Drapers for their munificent offer to erect a new 

 building for the Radcliffe Library at the expense of i5,ckx)/. 



Cambridge.— Prof. Fitzgerald, of Dublin, has been ap- 

 pointed an Examiner for the Adams Prize, in the place of the 

 late Mr. E. J. Stone. 



The Senior Wrangler is Mr. W. H. Austin, of Trinity. Six 

 out of the first seven Wranglers are from the same College. In 

 Part II. of the Tripos, Messrs. Barnes and Wilkinson, of 

 Trinity (bracketed second, 1896), and Mr. Houston, of St. 

 John's (bracketed fifth, 1896), are placed in the first division, 

 the Senior Wrangler of last year being in the second division. 

 No ladies are classed as Wranglers this year. 



It is stated in the American Naturalist that work will soon 

 be in full progress on the erection of a portion of the new 

 Museum of Archaeology and Palaeontology, for the University of 

 Pennsylvania. A botanical garden, covering ten acres, will be 

 laid out around the museum. The site of the structure was 

 ceded to the University by the city on condition that a museum 

 of art and science, surrounded by a botanical garden, be erected 

 on it. The portion to be erected immediately will cost not less 

 than 500,000 dols., while the cost of the whole building will 

 amount to 4,000,000 dols.. 



