CHAPTER VI. ALTERNATING MAGNETIC FLUX DISTRIBUTION. 355 

48. Magnetic screening by secondary currents in alternating 

fields. 355 

49. The differential equations of alternating magnetic flux 

in a lamina. 356 

50. Their integral equations. 357 

51. Terminal conditions, and the final equations. 358 

52. Equations for very thick laminae. 360 

53. Wave length, attenuation, depth of penetration. 361 

54. Numerical example, with frequencies of 60, 1000 and 

10,000 cycles per second. 362 

55. Depth of penetration of alternating magnetic flux in 

different metals. 363 

56. Wave length, attenuation, and velocity of penetration. 365 

57. Apparent permeability, as function of frequency, and 

damping. 366 

58. Numerical example and discussion. 367