520 Prof. Plucker on the Nature of the 



made in the same manner as in the second series, only that 

 weights were first laid on before the sand was added. 



In the last two series of weighings the large electro-magnet 

 was made use of; a very blunt cone, whose base was of the same 

 diameter as the electro-magnet, and whose point was rounded, 

 being placed upon the flat pole of the magnet. The buttons 

 were hung upon one of the arms of a common balance, and after 

 partially balancing the attraction by weights placed upon the' 

 opposite scale-pan, the separation was finally effected by the ad- 

 dition of small grains of shot. The electro-magnet was at one 

 time excited by a single cell of Grove, and again by a battery of 

 six cells. 



4. First Series of Experiments. 



The numbers express the weights in grammes necessary to pro- 

 duce the separation ; those side by side are the weighings of the 

 same button, repeated immediately one after the other. The 

 succession in which the different buttons were weighed is stated 

 in the first vertical column, the substance of the button used in 

 each case being indicated. 



6. Thwd Series. 

 The attraction of the different buttons by the strongest of the 

 three steel magnets was determined twice on different days. 



