ACTION OF POINTS. 589 



appears insensibly ; but if the finger be brought near to 

 the spherical side of the conductor, the electricity does 

 not escape until the finger has arrived within a small 

 distance, and then the greater portion of the electricity 

 escapes into the finger in one instant, as a spark large 

 enough to be heard and seen, and often also to be dis- 

 tinctly felt. 



The action of a point may also be shown if an elec- 

 trified body is brought near a neutral body to which the 

 point is attached. Let a fine sewing needle be fixed in 

 a cork and the cork placed upon the electroscope, so 

 that the point of the needle is directed upwards. If the 

 electroscope has a round knob, the cork may be attached 

 to it by making with the cork -borer a hole in the lower 

 side of the cork, about l cm deep, into which the knob fits. 

 When a rubbed glass rod is held about 20 cm above the 

 point of the needle, electrical separation takes place by 

 induction, in the same manner as it takes place in an 

 electroscope without a pointed extremity; negative 

 electricity is attracted to the point, and positive is 

 repelled to the leaves. But if after a short time the 

 glass rod is taken away without having touched the 

 electroscope, the leaves will not collapse as they would 

 under ordinary circumstances : the electroscope is 

 charged. The nature of the charge may be investigated 

 by pushing the cork off the knob, with an unelectrified 

 insulator, for example a rod of glass or sealing-wax, so 

 as to render the action of the point no longer possible, 

 and bringing the rubbed glass rod which was used in 

 the experiment near the electroscope The leaves will 

 diverge more widely, thus indicating that the electricity 

 is of the same kind as that of the glass rod. The elec- 



