demonstrating a limit to the Magnetizahility of Iron. 455 



results of some experiments in the following table, the first 

 column of which contains the forces to which the electro-magnet 

 had been exposed ; the second, the lifting powers due to those 

 forces; and the third, the lifting power left after the circuit 

 was broken. ^ 



Table VI. ,U 



There was considerable difficulty in observing the smaller lift- 

 ing powers. Nevertheless it is certainly the case, that the power 

 retained after the circuit was broken was very nearly equal to the 

 lifting power, with small electric forces. 



When the whole current is not entirely cut ofi", but merely 

 reduced in intensity by the interposition of a bad conductor, a 

 surprising quantity of magnetism may be supported by a very 

 small electric force. I subjected No. 1 to an electro-magnetic 

 force of 90, a quantity adequate to bring its power up to 560 lbs., 

 and then reduced the current to different degrees of intensity. In 

 the following table, the first column contains the electro-mag- 

 netic force to which the force of 90 was reduced ; the second 

 expresses the lifting power which is simply due to those quan- 

 tities ; and the third gives the lifting power which the same 

 quantities could support. 



Table YII. 



Electro-mag- 

 netic force. 



31 



21 



14-5 

 6-2 

 41 



Lifting power. 



45 



23 



10 

 2-6 

 l-l 



Supported lifting 

 power. 



294 



210 



112 



63 



56 



A battery of the size of a common thimble was quite sufficient 

 to produce an electro -magnetic force of 31 in the coil of No. 1, 

 and consequently to sustain a magnetic attraction of about 300 

 lbs. j and it is easy to perceive, that by increasing the size of the 

 electro-magnet and the quantity of its coils, the same minute 

 source could support a magnetic virtue of indefinite amount. 

 ^ ^ ^ jj{ ^ ^ 



Broom Hill, near Manchester, 

 August 21, 1840. 



