Al'RIL, 1911. 



KNOWLEDGE. 



159 



surrounding the coin common 

 cross in another (see Figure 3). 



to the arms of the 



Fig I' UK J. 

 Coins arran.!;ed in the foi in of a cross. 



One specially interesting photograpli (l-"igure 4) is 

 perhaps that which shows a single coin and seven 

 small dots. This was taken h\ connecting oni> 

 terminal witii the coin, then placing some small 

 shot on the plate (the dots) at different distances, 

 and hnall}' connecting the other terminal with a ring 

 of brass wire about six inches in diameter and 

 concentric with the coin. The discharge was passed 

 for one second and the plate then developed. 



The corona riunul the coin at once calls to mind 

 the solar corona, and the luminosities attached to 

 the shot suggest comets' tails. Each shot has two 

 fans of light, a broad one pointing away from 

 the centre, which is larger as the shot is nearer. 

 and a narrower sheaf connecting the shot with 

 the coin, which dies out with increase of distance 

 much more rapidly than what ma}- be called the 

 outer tail. 



Without trying to found any argument as to the 

 nature of comets" tails and the light sometimes seen 

 pointing from a nucleus towards the sun, the 

 pictures are certainly very suggestive, and the actual 

 discharge as seen by the e}-e is much more strongly so. 



However, space in these pages is valuable, and 

 enough has been said. The phenomena are in the 

 main only what the known facts of the brush 

 discharge would suggest, except that I feel sure no 

 one would hiwe supposed that it would be possible 

 to reproduce such detail without the use of any lens 

 or camera. 



Inductoscripts, electrographs. or mere contact 

 photographs, whiche\-er they may he, I tliink they 

 are interesting enougli and curious enough to be 

 made more common kn(.iwledge. 



The apparatus I used w as an induction coil giving a 

 six-inch spark. \>\' which two medium-sized Leyden 

 jars were charged. The discharge from these was 

 then sent through the primary of a small oil-insulated 

 transformer, and the length of the spark gaj) adjusted 

 until the wires from the terminals of the transformer 

 were as luminous as it seemed jjossible to make 

 ihem. 



The coil, jars, and spark gap were covered Iw a 

 kirge cardboard box so that the photograjihic plate 

 was not logged b\' stra\' light, but was exposetl ouK^ 

 to the action to be exaniinecL 



Fiouui; 4. 

 Seven shot surrounding a coin. 



