Apbil 1, 1896.] 



KNOWLEDGE, 



73 



LONDON: APRIL 1, 1896. 



CONTENTS. 



Electpography : or the New Photography. By J. W. 



GiFFOKD. (Illustrated) 



Novel Experience with Rontgen Rays 



Aluminium: Its History, Manufacture, and Future. — I. 

 Uy Samuel KiDEAL, D.Sc.Lond., F.I. C. 



Waves. — IV. Ship Waves, and the Solitary Wave. Bj- 

 YArCHAX COESISH, M.Sc. (Illustrated) .". 



Notices of Books 



Science Notes , 



Letters: — II. Staniet Williams; W. E. Beslbt; W. Ltox 



BkOW>E, Jun. ; I. G. OrSELET 



Pliny and Cuvier. Bv E. Waiter MArxDEB, F.R.A.S. 

 (Plate) ■ 



The Spectrum of Helium. Bv E. Waltek ilAryDER, 

 F.R.A.S. (niustrated) ..." 



The Birch. By George Paxtox. (Illustrated) 



Greek Vases. — II. A. — Vases of the Primitive Period, 

 to 600 B.C. Bv H. B. Walters, M.A., F.S.A. 

 (Illustrcfed) ... ' 



The Face of the Sky for April. By Heebeet 

 Sadleb, F.R.A.S 



Chess Column. By C. D. Looock, B.A.Oion. 



ELECTROGRAPHY ; OR THE NEW 

 PHOTOGRAPHY. 



By J. W. GiFFORD. 



THE extreme interest taken by tlie public in this 

 subject, and the difficulty of obtaining reliable 

 information about it, must be my excuse for 

 venturing to write of what is still so little under- 

 stood. Most of those engaged in experiment are 

 too busy, and too eager to try for new eli'octs, to care to 

 spend their time in writing. When the news of Prof. 

 Kontgen's wonderful application of this form of electric 

 force first reached this country, it was received with doubt 

 by some ;ind with scorn by others. Now we believe and 

 have seen what would have seemed too absurd for a work 

 of fiction a few years ago. Not only can coins enclosed in 

 a box, or laid under a pie-dish, be electrographed with 

 perfect ease, but bones enclosed in living flesh can be 

 shown with little more difficulty. Any imperfection in 

 the bones, any foreign body in the tlesh, is made as 

 clearly visible as though laid bare by the surgeon's knife. 

 Hitherto, this can only be said to have been done to 

 perfection in the case of the hand or foot, but when we 

 remember that the first news of Prof, llontgen's experi- 

 ments reached us but a few weeks ago, the only marvel ia 

 that so much has already been accomplished. 



The earliest experimenters in England who attained 

 satisfactory results by the new influence — call it what you 



will — were Mr. A. A. Swinton, in London, and myself at 

 Chard. 



Shortly before the article appeared in the Standard last 

 January announcing Prof. E6ntgen"s discovery, I had been 

 experimenting with spectrum photo.graphy, and for this 

 purpose had bought a hand dynamo and a large spark coil, 

 so as to volatilize the more refractory elements. Some 

 fifteen years ago, when Prof. Crookes' researches on 

 radiant matter were first published, I had bought a set of 

 Crookes tubes, and therefore found myself equipped, by 

 good fortune, with all the necessary material for making 

 the experiments. But so imbued was I with the idea of 

 spectrum analysis and spectrum photography, the study 

 of which had engaged my attention for years, that no 

 explanation of the discovery other than a photographic one 

 occurred to me. I therefore tried a set of experiments — 

 all of which failed — taking as my standpoint the idea that 

 the photographs must be produced by ultra-violet rays. 

 Thinking the thing was a hoax, or at any rate a mis- 

 conception, and seeing that the experiments in Vienna 

 had, up to that time, failed, I sent a communication to the 

 Royal Photographic Society, detailing my experiments and 

 their failure. This arrived just too late for the meeting 

 on the 14th of January. 



After that the papers became more definite, and I tried 

 again, this time abandoning the theory of light for that of 

 electricity ; and on Saturday the 18th, to my great delight, 

 I succeeded in electrographing a child's hand through 

 cardboard. This was shown at the Photographic Meeting 

 on the following Tuesday. In this early experiment, and 

 in fact in all the earlier ones, the plate was enclosed in 

 a cardboard box, such as photographic plates are packed in, 

 and the hand laid on the lid of the box about two inches 

 below the glass bulb — for, as far as appearance goes, tube 

 is a misnomer — with the result that a child's hand appeared 

 on the plate after development. In the earlier attempts 

 five minutes' exposure was given, and in the first successful 

 one the nails appeared, but little or no bone. Never since 

 the first experiment have the nails appeared — why is not 

 known. Probably the bones did not appear partly because 

 it was a child's hand and the ossification imperfect, and 

 partly because the exposure was too short for the power 

 used. Later experiments have shown better results, and 

 for the benefit of those who have never seen the apparatus 

 at work I wUl describe what is used. 



First there is a hand dynamo, giving a current of ten 

 volts, fifteen amperes ; then a spark or intensity coil, giving 

 a ten-inch spark ; and lastly the glass bulb, which is 

 exhausted to about the millionth of an atmosphere. Of 

 course every man has his own fad, but I believe all the 

 most successful experimenters have used apparatus similar 

 to this. The difi'erent parts of the apparatus are connected, 

 the circuit closed, and the dynamo revolved. The bulb is 

 filled with a beautiful green light, which looks a very 

 yellowish green by daylight — a colour difficult to describe, 

 but characteristic of this state of exhaustion. Tubes less 

 exhausted show a whitish or violet light, and more 

 exhausted they do not allow the spark to pass freely 

 enough to do the work. The greenish light is, as far as my 

 experience goes, a sine qu<! non. The tube in the later 

 experiments has been placed about eight inches from the 

 object to be photographed, and this, though it lengthens 

 exposure, vastly improves definition. 



One must leave off thinking of these pictures as photo- 

 graphs, and think of them and reason about them as 

 shadows. If a mateh be lighted and the blade of a knife 

 be held up between it and the wall, definition improves and 

 the size of the shadow decreases as the knife is farther 

 from the match and closer to the wall. This simple 



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