Mar., 1904.] 



KNOWLEDGE c^- SCIENTIEIC NEWS. 



Sinsjle and multiple discharges were discussed ; the 

 former occupying a very short space of time, possibly 



about of a second. Numerous representations of 



20.000 '^ 



sparks taken under different conditions were shown, and 



Single Discharg:c bL-twccn Points. 



attention was called to the marked difference between 

 the positive and negative discharge, the former having a 

 brush-like appearance, and the latter invariably showed 

 a characteristic fern-like representation on the plate. 



The lecturer showed excellent examples of the in- 

 creased intensity of the spark when a spark gap was 

 introduced into the secondary circuit, and in passing re- 



.Single Positive Discharge on Florir. 



marked that this was the e.xplanation of the use of a 

 spark gap employed in connection with the sparking 

 plug of motor vehicles. 



Examples of sparks from brushes and spheres, in addi- 

 tion to ordinary point discharges, revealed many extra- 

 ordinary effects ; and in all the characteristic features of 



the positi\e and negative discliarges were invariably 

 present. The results. Dr. Kodman cxphiined, were 

 obtained on Imperial platfs, wliicli were subsiMiuentiy 

 developed in the usual manner with a pyio suda 

 solution. 



The production of the photographic image of 

 coins placed on the surface of the emulsion, and 

 connected up with one or other terminals of 

 the coil furnished some highly interesting 

 results; and in these cases the characteristic 

 features of the positive and negative discharges 

 were well shown. 



On passing a single discharge on these coins 

 with subsequent development of the latent 

 image, a very distinct representation of the coin 

 with its inscription clearly legible was produced, 

 and the same effect was obtained in a much 



Single Negati\e Discllarge on Coin. 



clearer manner when a multiple discharge of 

 current extending to i-2oth sec. was used. 



In this experiment when a discharge was 

 produced with two coins attention was called 

 to the remarkable appearance that the plate on 

 development presented — the image of botli 

 coins being multi])le. Dr. Rodman stated that 

 he had up to the present been unable to deter- 

 mine the cause of these multiple images, and, 

 in order to arrive at a conclusion as to the 

 cause of these nimbus-like shadows, had adopted 

 various devices, but had failed with them to elucidate 

 the matter. 



Assuming that they were the result of reflection, films 

 had been used instead of the glass plates employed in tlie 

 other experiments. Backed plates had also been made 

 use of, but the multiple shadows still presented them- 

 selves. To exclude the possibility of their being pro- 



