Machine for producing High Tension Electricity. 183 



action is very strong, as it is near the sparking terminals, the 

 external molecules of the metal are themselves shot off, as is evident 

 from the fact that the positive wire becomes reduced to a neck a little 

 in rear of the sparking end when subjected to a prolonged succession 

 of Leyden battery discharges. It is also well known that if a dis- 

 charge from a powerful Leyden battery is sent through a very fine 

 wire, the whole wire is exploded. Under ordinary conditions the 

 cohesion of the molecules restrains their movement within very 

 narrow limits, and confines their action to mere impulse on the sur- 

 rounding air. Now, it appears to me that we may regard the track 

 of the spark as a line of conducting air, which, having no cohesion 

 to keep its molecules together, is exploded at every discharge, and, 

 consequently, produces a far greater amount of dispersion than the 

 wire. The force* of the lateral discharge at short distance is very 

 great. In all cases the dust beneath the conducting wires was struck 

 into the card, so as to leave a permanent delineation of the wire. 

 The dust also over all parts of the figure, where the action was 

 strong, was forced into the card, so as to leave a stain after the loose 

 dust was shaken off, and thus a stained picture of remarkable 

 accuracy, embracing the greater part of the figure, was in some cases 

 preserved. 



In all the figures the emanations from the positive and negative 

 wires are of the same character, but present a great superiority of power 

 011 the positive side. This superiority is, however, much greater in 

 the case of coil discharges than in battery discharges. This may be 

 attributed to the oscillations between the inside and outside coatings 

 of the Leyden jars suffering far less degradation than those between 

 the terminals of the coils. If there were no degradation, the forces 

 exerted on the positive and negative side would be equal and ever- 

 lasting. The application of wet string to the battery lessens the 

 difference between these opposite forces, but it augments the lateral 

 displacement of dust from both wires while it diminishes the explo- 

 sive force of the spark. 



Diagrams of the dust figures are annexed (Plates 2 13), but, 

 though admirably drawn, they necessarily fall short of the photo- 

 graphs in showing the delicate lines and shadings of the actual 

 figures. To suit the pages of the ' Proceedings,' the diagrams are 

 reduced to about half the size of the originals, but the exact scale is 

 marked on each. The following is a descriptive list of the figures : 



No. 1 was produced by a succession of sparks from six combined 

 coils discharged simultaneously. The tracks of the sparks, the sur- 

 rounding circular lines, the impress of the positive and negative 



* In one case I knocked a large piece out of the bottom of a thick glass trough, 

 containing only an inch depth of water, by discharging an under-water spark along 

 the bottom. 



