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



1595. When the phenomena of currents are observed in dense insulating dielectrics, 

 they present us with extraordinary degrees of mechanical force. Thus, if a pint of 

 well rectified and filtered (1571.) oil of turpentine be put into a glass vessel, and 

 two wires be dipped into it in different places, one leading to the electrical machine, 

 and the other to the discharging train, on working the machine the fluid will be 

 thrown into violent motion throughout its whole mass, whilst at the same time it will 

 rise two, three, or four inches up the machine wire, and dart off in jets from it into 

 the air. 



1596. If very clean uninsulated mercury be at the bottom of the fluid, and the wire 

 from the machine be terminated either by a ball or a point, and also pass through a 

 glass tube extending both above and below the surface of the oil of turpentine, the 

 currents can be better observed, and will be seen to rush down the wire, proceeding 

 directly from it towards the mercury, and there, diverging in all directions, will ripple 

 its surface strongly, and mounting up at the sides of the vessel, will return to re-enter 

 upon their course. 



1597- A drop of mercury being suspended from an amalgamated brass ball, pre- 

 served its form almost unchanged in air (1581.) ; but when immersed in the oil of 

 turpentine it became very pointed, and even particles of the metal could be spun 

 out and carried off by the currents of the dielectric. The form of the liquid metal 

 was just like that of the syrup in air (1584.), the point of the cone being quite as fine, 

 though not so long. By bringing a sharp uninsulated point towards it, it could also be 

 eflfected in the same manner as the syrup drop in air (1587-)? though not so readily, 

 because of the density and limited quantity of the dielectric. 



] 598. If the mercury at the bottom of the fluid be connected with the electrical 

 machine, whilst a rod is held in the hand terminating in a ball three quarters of an 

 inch, less or more, in diameter, and the ball be dipped into the electrified fluid, very 

 striking appearances ensue. When the ball is raised again so as to be at a level nearly 

 out of the fluid, large portions of the latter will seem to cling to it (fig. 24.). If it 

 be raised higher, a column of the oil of turpentine will still connect it with that in the 

 basin below (fig. 25.). If the machine be excited into more powerful action, this will 

 become more bulky, and may then also be raised higher, assuming the form fig. 26 ; 

 and all the time that these eflTects continue, currents and counter-currents, sometimes 

 running very close together, may be observed in the raised column of fluid. 



1599. It is very difficult to decide by sight the direction of the currents in such 

 experiments as these. If particles of silk are introduced they cling about the con- 

 ductors ; but using drops of water and mercury the course of the fluid dielectric seems 

 well indicated. Thus, if a drop of water be placed at the end of a rod (1571 .) over the 

 uninsulated mercury, it is soon swept away in particles streaming downwards towards 

 the mercury. If another drop be placed on the mercury beneath the end of the rod, 

 it is quickly dispersed in all directions in the form of streaming particles, the attract- 

 ive forces drawing it into elongated portions, and the currents carrying them away 



