RECENT PROGRESS IN PHYSICS. 



379 



"Take next ad ro]i of strong solution of miiriateoflime; being 

 electrified, a part will probably be dissipated, but a con- 

 siderable portion, if the electricity be not too powerful, will 

 remain, forming a conical drop, (fig. 74,) accompanied by 

 a strong wind. 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." 



" With a drop of water the effects were of the same kind, and 

 were best obtained when a portion of gum water or syrup hung 

 from a ball, (fig. 75.) When the machine was worked slowly a fine, 

 large, quite conical drop, with concave lateral outline and a Fig. 75. 

 small rounded end, was produced, on which the glow appeared, 

 whilst a steady wind issued from the point of the cone of 

 sufficient force to depress the surface of uninsulated water 

 lield opposite to the termination. When the machine v/as 

 worked more rapidly some of the water was driven off, the 

 smaller pointed portion left was roughisli on the surface, 

 and the sound of successive brush discharges was heard, 

 Witb still more electricity, more water was dispersed ; that which re- 

 mained was alternately elongated and contracted,'"' and "a stronger 

 brush discharge was heard. Whea 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 the water beneath was attracted rather than driven away, and 

 the current of air ceased." — (1584.) 



" 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, thus : A sharp point being held opposite the coni- 

 cal drop, the latter soon lost its pointed form, was retracted and be- 

 came round ; the current of air from it ceased, and was replaced by 

 one from the point beneath, which, if the latter was held near enough 

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

 With still worse conductors, as oil, or oil of turpentine, the fluid was 

 "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 changed state as the particles of air, and, 

 not being able to discharge to them in a much greater degree than 

 the air particles themselves could do, were carried oft" 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." — (1588.) 



"A drop of gum water in the exhausted receiver of the air pump 

 was not sensibly affected in its form when electrified/' which was 

 partly owing to the diminished current of air, and partly, perhaps, that 

 the tension of the electricity on the ball is not so great in rarefied as 

 in dense air. 



" That I many not be misunderstood," says Faraday, " I must ob- 

 serve here that I do not consider the cones produced as the result only 

 of the current of air or other insulating dielectrics over their surface. 

 When the drop is of badly conducting matter a part of the effect is 

 due to the electrified state of the particles," &c. — (1594.) 



