CONVECTION, OR CARRYING DISCHARGE — EFFECTS OF FLUID DROPS. 147 



1581. Conducting fluid terminations, instead of rigid points, illustrate in a very 

 beautiful manner the formation of the currents, with their effects and influence in 

 exalting the conditions under which they were commenced. Let the rounded end of 

 a brass rod, 0*3 of an inch or thereabouts in diameter, point downwards in free air; 

 let it be amalgamated, and have a drop of mercury suspended from it ; and then let 

 it be powerfully electrized. The mercury will present the phenomenon of glow ; a 

 current of air will rush along the rod, and set off" from the mercury directly down- 

 wards ; and the form of the metallic drop will be slightly aff'ected, the convexity at 

 a small part near the middle and lower part becoming greater, whilst it diminishes 

 all round at places a little removed from this spot. The change is from the form 

 of a (fig. 21.) to that of ^, and is due almost, if not entirely, to the mechanical force 

 of the current of air sweeping over its surface. 



1582. As a comparative observation, let it be noticed, that a ball gradually brought 

 towards it converts the glow into brushes, and ultimately sparks pass from the most 

 projecting part of the mercury. A point does the same, but at much smaller di- 

 stances. 



1583. Take next a drop of strong solution of muriate of lime ; being electrified, a 

 part will probably be dissipated, but a considerable portion, if the electricity be not 

 too powerful, will remain, forming a conical drop (fig. 22.), accompanied by a strong 

 current. If glow be produced, the drop will be smooth on the surface. If a short 

 low brush is formed, a minute tremulous motion of the liquid will be visible ; but 

 both eflfects coincide with the principal one to be observed, namely, the regular 

 and continuous charge of air, the formation of a wind or current, and the form 

 given by that current to the fluid drop. If a discharge ball be gradually brought 

 toward the cone, sparks will at last pass, and these will be from the apex of the cone 

 to the approached ball, indicating a considerable degree of conducting power in this 

 fluid. 



1584. With a drop of water, the effects were of the same kind, and were best ob- 

 tained when a portion of gum water or of syrup hung from a ball (fig. 23.). When 

 the machine was worked slowly, a fine large quiet conical drop, with concave lateral 

 outline, and a small rounded end, was produced, on which the glow appeared, whilst 

 a steady wind issued, in a direction from the point of the cone, of suflScient force to 

 depress the surface of uninsulated water held opposite to the termination. When the 

 machine was worked more rapidly some of the water was driven off"; the smaller 

 pointed portion left was roughish on the surface, and the sound of successive brush 

 discharges was heard. With still more electricity, more water was dispersed ; that 

 which remained was elongated and contracted, with an alternating motion ; a stronger 

 brush discharge was heard, and the vibrations of the water and the successive dis- 

 charges of the individual brushes were simultaneous. When water from beneath 

 was brought towards the drop, it did not indicate the same regular strong contracted 

 current of air as before; and when the distance was such that sparks passed, 



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