148 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIII.) 



the water beneath was attracted rather than driven away, and the current of air 



ceased. 



1585. When the discharging ball was brought near the drop in its first quiet glow^ 



ing state (1582.), it converted that glow into brushes, and caused the vibrating 

 motion of the drop. When still nearer, sparks passed, but they were always from the 

 metal of the rod, over the surface of the water, to the point, and then across the air 

 to the ball. This is a natural consequence of the deficient conducting power of the 

 fluid (1584. 1585.). 



1586. Why the drop vibrated, changing its form between the periods of dis- 

 charging brushes, so as to be more or less acute at particular instants, to be most 

 acute when the brush issued forth, and to be isochronous in its action, and how the 

 quiet glowing liquid drop, on assuming the conical form, facilitated, as it were, the 

 first action, are points, as to theory, so evident, that I will not stop to speak of them. 

 The principal thing to observe at present is, the formation of the carrying current of 

 air, and the manner in which it exhibits its existence and influence by giving form to 

 the drop. 



1587. That the drop, when of water, or a better conductor than water, is formed 

 into a cone principally by the current of air, is shown amongst other ways (1594.) 

 thus. A sharp point being held opposite the conical drop, the latter soon lost its 

 pointed form ; was retracted and became round ; the current of air from it ceased, 

 and was replaced by one from the point beneath, which, if the latter were held near 

 enough to the drop, actually blew it aside, and rendered it concave in form. 



1588. It is hardly necessary to say what happened with still worse conductors than 

 water, as oil, or oil of turpentine ; the fluid itself was then spun out into threads and 

 carried off*, not only because the air rushing over its surface, helped to sweep it away, 

 but also because its insulating particles assumed the same charged state as the par- 

 ticles of air, and, not being able to discharge to them in a greater degree than the 

 air particles themselves could do, were carried off" by the same causes which urged 

 these in their course. A similar effect with melted sealing-wax on a metal point 

 forms an old and well-known experiment. 



1589. A drop of gum water in the exhausted receiver of the air-pump was not 

 sensibly aff^ected in its form when electrified. When air was let in, it began to show 

 change of shape when the pressure was ten inches of mercury. At the pressure of 

 fourteen or fifteen inches the change was more sensible, and as the air increased in 

 density the eff*ects increased, until they were the same as those in the open atmo- 

 sphere. The diminished effect in the rare air I refer to the relative diminished energy 

 of its current ; that diminution depending, in the first place, on the lower electric 

 condition of the electrified ball in the rarefied medium, and in the next, on the atte- 

 nuated condition of the dielectric, the cohesive force of water in relation to rarefied 

 air being something like that of mercury to dense air (1581.), whilst that of water 

 in dense air may be compared to that of mercury in oil of turpentine (159/.). 



