Dr. Hare's Electrical Machine, &fc. 



27T 



It remains to show why a large mass of electric matter will be 

 discharged in a spark when there is sufficient proximity, although 

 that electric matter be situated in the large globe, and attracted by 

 the other, under circumstances in which, as above stated, it would 

 not pass without that proximity. 



It must be evident that attraction increases, as the distance be- 

 tween the bodies which exercise it lessens. Of course the attraction 

 of the small globe must always act more powerfully on those portions 

 of the electric fluid, which occupy the nearest parts of the positively 

 excited globe. But this difference of distance, and consequent di- 

 versity of attraction, increases as the globes are approximated. Thus 

 that portion of the electric fluid which sustains this pre-eminent at- 

 traction, will be accumulated into a conoid; the acuteness of which, 

 and attraction causing the acuteness, increasing with the proximity, 

 there will at last be sufficient projectile and penetrative power to 

 break through the air, and thus open a passage for the whole of the 

 quantity attracted by the small negatively excited globe. 



When, by the process last described, the fluid is made to leap 

 through a comparatively small interval, by the concentrated attrac- 

 tion exercised by a small negative ball upon the extensive surface of 

 the electric matter diffused through a large globe, the air does not 

 become sufficiently condensed to resist it before it reaches its desti- 

 nation, and, of course, it cannot assume the erratic form which would 

 arise from repeated changes in its course, as in the instance of the 

 long spark. 



Of the Electrical Brush. 



When the machine is in active operation, and the 

 prime conductor insulated ; from a small knob at- 

 tached to it, as at B, in the figure, the electricity 

 will be sent off, as by the concomitant light to ex- 

 hibit the form of a luminous brush, as represented 

 in this figure at B. For the production of this phe- 

 nomenon, it is necessary that the electric fluid shall 

 be condensed into a small prominent mass, so as, 

 agreeably to the preceding explanation, to have great 

 penetrating power. This it cannot possess, when, 

 with the same intensity in the generating power, a large ball is posi- 

 tively electrified. In that case, the electric column presents a front 

 too broad to procure a passage through the surrounding non-con- 



