296 On Dynamo- and Magneto- Electric Machines. [Nov. 20 r 



together, and then the armature was forced off, the needle would 

 swing 20° and fall back to 5° very slowly (in about fifteen minutes). 



If both poles of the \J magnet were caused to be of the same name, 

 and the armature placed upon them, there was no attraction after 

 breaking battery contact. 



The straight cores, if placed upon the (J magnet connected by the 

 armature, and then magnetised in such a way that the poles of the cores 

 faced like poles of the U magnet, retained no magnetic polarity when 

 taken away from the system, whereas when they formed part of such 

 a closed circuit as we have above described, the bars retained sufficient 

 polarity to affect a magnetic needle for some time. 



We may here remark that the attractive force of electro-magnets 

 for each other, in what we call open circuit, is not nearly as great as 

 in a closed circuit. For instance, the U magnet could not be lifted 

 by the straight cores placed upon its poles, even with a current from 

 six Bunsen cells running round the helices ; but on bridging the circuit 

 with the armature the whole mass, weighing 82 lbs., could be raised 

 from the ground with the current of only two cells, and quite irre- 



