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XIV. 



NOTE ON LAMINATED MAGNETS. 



By WILLIAM BEOWN, B.Sc, 

 Professor of Applied Physics, Boyal College of Science for Ireland, Dublin. 



[Read May 23. Published June 19, 1916.] 



In his "Magnetical Investigations," 1839, Scoresby gives some results 

 obtained with laminated magnets when the laminations were in contact, 

 and when they were separated by pieces of wood varying in thickness from 

 0'14 of an inch to 1 inch ; and he shows that when the plates or laminations 

 are separated there results a stronger magnet than when they are in contact. 

 Jamin 1 also worked with laminated magnets with respect to the carrying 

 power and distribution of magnetism. The present writer has not been able 

 to find any past or recent work which gives experimental data on how the 

 apparent distance between the poles of a straight magnet varies with the 

 number of laminations composing the magnet, and this note gives the results 

 of some experiments on this subject. The laminations were made out of a 

 piece of clock-spring steel, cut into strips 10 cms. long, 0"5 cm. wide, and 

 - 06 cm. thick. They were made glass-hard by being raised to a bright red 

 heat in a muffle furnace, and then dropped end on into a vessel of cold water 

 three feet deep ; and in order to keep them as straight as possible in the 

 hardening process they were fixed between two pieces of square-section steel 

 rod. When cleaned up and polished each strip weighed very approximately 

 2*33 grammes. 



These laminations were taken in sets consisting of 1, 2, 3, 5, 7, 10, 15, 

 and 20 strips respectively, each set was magnetised, as explained below, in 

 the same magnetic field, and the magnetic moment and apparent distance 

 between the poles measured. The tests were made (1) when the laminations 

 were all in actual contact ; (2) when the laminations were separated by pieces 

 of paper of the same length and width as the lamination, and of thickness 

 - 015cm., 0'03 cm., and - 06cm. respectively, that is, there were four sets of 

 experiments made in all. 



The magnets when being tested were fi xed in a non-magnetic brass holder, 

 which clamped the combination at each end and also at the middle. The 



1 Compt. Rend., Tome lxxv, lxxvi, lxxvii, lxxxi. 1872-75. 



SOIENT. PROC. R.D.S., VOL. XV., NO. XIV. Z 



