ELECTROGRAPHS. 



r.y A. \\". CLAYI)i:X. M.A.. 



Priiulpal of t/ic h'dYiil Albert Mciimriiil i'iiivcri;ity Colhiic. lixcfcr. 



Se\"1-:kai. years a,t;o. when eN|iL'nniciitin,i; with an 

 early form of Tesla apparatus suppheil to the 

 College by Mr. Apps, I hit ujion a phenomenon 

 which deserx'es to be better known. At that time 

 I belie\'ed the results were novel, but when I came 

 to describe them I found that similar observations 

 had been made hv Mr. 1'. ]. Smith at Trinit\- 



I'lr.i'Ri; 1. 



EK-ctrograph of a kaj,'L' coin (blaned iniagul rrstint,' upon 

 two small iiifdals. 



College, O.xford, and described b\- him (.)n June 24th. 

 1892, to the Physical Society under the title 

 " Inductoscript." His method was to place a coin 

 or medal upon a photographic plate which rested on 

 a conductor, and then connect the coin and conductor 

 with the poles of an " Inductorium "' or Transformer 

 for a time varj-ing from five seconds to fifty seconds. 

 On development the details of the face of the coin in 

 contact with the film were revealed. His paper 

 appears in X'nluiiie XI of the Proceedings of the 

 Physical Society, but unfortunateh" it is not 

 illustrated by any reproductions of the photographs. 



Seven years later, struck In- the beaut\- of the 

 discharge from the Tesla transbjrmer, it occurred to 

 me that if a number of metal bodies were to be 

 placed upon a sensitive plate it should be possible to 

 get some sort of reproduction of the surrounding 

 discharges. 



If, for instance, a brass sheet is laid on the 

 working bench, then a plate of glass, and a coin or 

 group of coins upon the glass, on connecting one of 

 the coins with one terminal of the transformer and 

 the brass plate to the other terminal the coins are 

 seen to be surrounded by beautiful radiating coronae 

 caused by the discharge, I therefore substituted 

 a jihotographic j)late, film side uppermost, tor the 

 glass and let the discharge [kiss for a second or two. 

 On developing, I was surprised to see that not only 



were tlie details of the radiating discharge far more 

 perfecth' rendered than I had e.xpected, but the 

 modelling of the A\hole face of the coin in contact 

 with the film was sharph' revealed. 



In order to get the detail it was necessary to have 

 the coin actualh' resting on the film. In some cases 

 it was lifted up a short distance, and the mere 

 tliicknessof a threepenny bit was found to be enough 

 to si)oil and blur the image. See Figure 1, in which 

 the central large coin rests upon the little medals. 



Mr. Smith attributed his photographs to the 

 electric current, or at least the electrification of the 

 rtlin. but in the case of my observations it is not easy 

 to sa\' whether the action on the film was due to the 

 discharge or to the light ol the discharge. A coin 

 under the conditions of the e.xperiment. that is to 

 saw in contact with one terminal of a Tesla 

 transformer, is luminous all over, and the longest 

 ra\s spring from the sharpest convexities, such as the 

 the edges of the milled ritu, in accordance with the 

 general rule as to the distribution of a charge on 

 conductor, 



I am inclined to think that this distribution of 

 the discharge is the real explanation of the phenom- 

 enon, though the effect on the silver salt may just as 

 well be electric as strictK' photographic. 



FiGCRK -'. 



The effect of the sparUs connecting coins and in the 

 square hole of the Japanese example. 



Howe\er this may be, the experiments are very 

 easy to make, verv beautiful to see, and yield results 

 of considerable interest. Note, for instance, the 

 sharp, slender sjjarks which connect the various 

 coins, the corona of ratliating siiarks surrounding 

 i-ach coin, and tlie wa\- in which these coronae 

 decline to join. This last featiu'e is especially well 

 shown in the scpiare hole in the Jaj^anese coin shown 

 ni one picture (F'igure '2), and in the discharge 



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