ELECTRICAL ATTRACTION. 553 



lias been well rubbed, electrifies far more readily than a piece of silk. 

 The amalgam is poisonous, and acts like mercury on gold and 

 silver. 



The piece of cloth upon which the amalgam has been spread 

 should be laid upon the palm of the left hand and on it the glass 

 rod which is held in the right hand. The left hand is then closed, 

 so that the cloth may completely embrace the glass rod, which, by 

 moving the right hand, is repeatedly drawn to and fro. Finally the 

 left hand is opened when the right hand is nearest to it. 



The cork ball is first cut into shape with a sharp knife (a razor is 

 the best for the purpose, but it soon becomes blnnt if the cork is not 

 quite sound and very soft), and then filed so as to be nearly round ; 

 it need not be exactly globular, but must have no edges or project- 

 ing points. The thread from which it is suspended is obtained by 

 untwisting common sewing thread, and using one of the several 

 filaments of which the whole consists ; such a filament is more 

 flexible than a twisted thread. One end is passed through the cork 

 ball by means of a fine needle arid secured by a knot at the other 

 end. The thread should be cut close to the knot and pulled so that 

 the knot disappears in the cork. 



Balls made of the pith of the elder tree are still better for these 

 experiments, and may be purchased at the dealers in electrical 

 apparatus. 



A small moveable ball suspended in the manner just described is 

 called an electrical pendulum. 



Even heavier bodies than pith or cork balls and small 

 pieces of paper may be set in motion by electrical at- 

 traction if they are suspended so as to move easily. 

 Two corks of about the same size are fixed to the ends 

 of a wire, 40 cm long and 2 mm thick, bent as in fig. 302 A, 

 and suspended in the middle by a very thin thread. If 

 an electrified glass rod is brought near to one of the 

 corks, the latter is attracted, and if the glass rod is con- 

 tinually moved in a circle away from the approaching 

 cork the wire with the corks will revolve round the 

 thread as axis. 



The electrified body itself, if freely suspended, may 

 be set in motion bv the attraction between it and an un- 



