508 ELECTRICITY. 



table, be brought within a third of an inch of each other, 

 and the thumb is pressed upon the table so as to touch 

 the two ends of the wire, and to cover the whole place 

 of the interruption, and a strong spark be passed through 

 the apparatus thus arranged, the flesh of the finger will 

 be strongly illuminated. 



The electric light exhibited in these various experi- 

 ments does not depend at all upon the nature of the sub- 

 stance which is charged. If a person stands upon the 

 insulating stool in the manner before described, and is 

 charged, sparks may be drawn from his hands, his face, 

 or any part of the body. A tumbler of water or a mass 

 of ice, may be charged, and sparks taken from its surfa- 

 ces. It is the simple passage of the electricity through 

 the air, which produces. the effect. 



Illuminated water. Although water is classed among 

 conductors, still the resistance it makes to the passage of 

 the electricity is such, that when it is made a part of the 

 circuit, a very distinct light is evolved. A moderate 

 charge will produce a bright spark when made to pass 

 .through water, and the spark is still more luminous in 

 oil, alcohol, or ether, which are worse conductors than 

 watejfijton the contrary, in fluids of greater conducting 

 power^there is greater difficulty in eliciting electric light. 

 Thus a much higher charge is required to produce a 

 spark in hot water than in cold ; a still higher in saline 

 solutions; and in concentrated acids light can be obtain- 

 ed only when their volume is very small ; so that it is 

 necessary for that purpose to draw aline of the acid upon 

 a plate of glass with a camel's hair pencil. This is il- 

 lustrated by the following experiment. Draw a line with 

 a pen dipped in. water efi -tbj|L surface of a slip of glass; 

 place one extremity of tho^pqie ' n contact with the coat- 

 ihg of 4 Leyden jar, and al six inches' distance place 

 upon the line one knob of the discharging rod. When 

 the jar is fully charged, bring the. other ball of the dis- 

 charged to the knob of the jar, and the discharge will 

 take place luminously over the six inches of water. Next, 

 trace a line with a pe/i dipped in sulphuric acid on a 

 slip of glass, as in the former experiment, and place one 

 extremity of it in contact with the outside of the jar ; the 



