312 



sure. It is not affected by the quantity of acid in the electro- 

 lyte, or the size of the electrodes ; it is by heat, and by the 

 intensity of the battery. The latter, however, he regarded as 

 only an apparent error, but had not yet fully investigated it. 



The results which he obtained were exhibited in a tabular 

 form, giving the lifting power, the residual magnetism, and the 

 residual excitation for 35 different currents from 0.04 to 6.85. 



The first of these is influenced by various circumstances. 



1 . A magnet requires its load to be gradually increased. 



2. It requires time for the full development of its power ; 

 with the highest current used, not less than five minutes ; with 

 the lower, fifteen. 



3. Like permanent magnets, its power is diminished by 

 temperature. He found that in this one the reduction is 0.00033 

 for each degree above 60°. 



4. It is influenced by the molecular change which produces 

 permanent magnetism, being greatest when that is least. 



It is not proportional in any part of the range included by 

 these experiments to the intensity of the exciting current, and 

 the ratio between them decreases very rapidly as the latter is 

 increased. From this fact it follows, that a magnet has a li- 

 mit beyond which its power cannot go, in this one probably 

 under 1000 lbs. A current 1 enables it to lift 500 lbs., and 

 one of 6.85 only 775. When the magnet has acquired perma- 

 nent magnetism, a feeble negative current (in the opposite 

 direction) will not destroy that condition, nor change the usual 

 direction of the polarity, but merely lessen the lift. With 

 higher powers these effects do take place ; but the negative 

 lifts are less than the other until they amount to half the 

 maximum (a point which seems critical in electro-magnetism). 

 This degree of excitation should, therefore, be used in all ma- 

 chines when the polarity is to be reversed. 



The maximum residual magnetism observed in this magnet 

 is 8.88 lbs., but in general only 4.44. By long excitation its 

 molecular constitution is sometimes disturbed, so that this 

 quantity is thus increased, but it recovers bv rest. 



