566 Dr. S. P. Thompson and Miles Walker on the 



Table showing Pull and Different Frequencies with various 



Currents. 



Exciting Current. 

 Amperes. 



Mean lines per 

 sq. centimetre. 



Pull, in grammes, 



with Continuous 



Current. 



Pull, in grammes, 



with Alternate 



Current. 



A. At a frequency 



of 30 periods per 



second. 





8 



2300 



280 



280 



125 



3600 



820 



820 



B. At a frequency 



of 60 periods per 



second. 





8 



2300 



280 



280 



10-2 



2900 



530 



550 



C. At a frequency 



of 90 periods per 



second. 





4 



800 



60 



60 



4-2 



1100 



100 



100 



10-2 



2900 



530 



530 



21 



5600 



2400 



2200 



D. At a frequency 



of 120 periods per 



second. 





132 



3900 



900 



900 



21 



5600 



2400 



2200 



These experiments show that the pull was exactly the same 

 when the intensity of the flux did not exceed 4000 lines per 

 square centimetre. At higher degrees of magnetization the 

 pull with alternate currents is slightly less. 



It may he remarked that at higher intensities and with 

 higher frequencies, eddy-currents, if any are present, will 

 produce, for an equal flow of exciting current, a greater 

 demagnetizing action, and therefore lessen the pull. On the 

 other hand, if the current is supplied at a constant (alternating) 

 voltage, eddy currents do not decrease the magnetization but 

 cause more current to flow in proportion. 



Another experiment was made with a solenoidal electro- 

 magnet with a laminated U-form plunger belonging to a 



