CONTENTS. xiii 



ART. PAGE 



57. Experiments on the induction of magnetism in soft iron by 



the action of a steel magnet 131 



58. Explanation of the attraction of soft iron by either pole of a 



steel magnet, as an effect of induction .... 133 



59. Rapid diminution, with increase of distance, of the attraction 



between a magnet and soft iron .*.... 134 



60. Induction of magnetism in soft iron, produced by terrestrial 



magnetism < 135 



61. Effect of the terrestrially-induced magnetism in a mass of soft 



iron which is carried round a compass, at the same level as 

 the compass, and with the same part of the ma&s always 

 directed to the compass-center 137 



62. Effect of the combination of two masses of iron, in opposite 



azimuths : and of two masses of iron, in azimuths differing 90 139 



63. Simplest form of theory for explanation of the phenomena of 



induction . . 139 



C4. The inductive energy may be resolted in different directions, 



in the same manner as statical forces ..... 141 



65. A mass of iron, symmetrical with respect to the plane directed 



to the axis of a compass and with respect to the horizontal 

 plane, and with its center at the same height as the compass, 

 is subject to terrestrial induction : theoretical investigation 

 of its deviating energy on the compass ; it follows the law 

 of sine 2 azimuth . . . . . . . .142 



66. Simpler investigation when the mass is spherical, with its 



center at the same height as the compass . . . .144 



67. In these cases, the magnitude of the deviation produced in 



the compass is independent of the magnitude of the terres- 

 trial horizontal force * . .146 



68. General investigation of the disturbing force produced by 



a mass of iron, symmetrical with respect to a vertical 

 plane passing through the compass-axis (as an iron-built 

 ship), subject to terrestrial induction 147 



69. Examination of the physical meaning of the different terms 



of the disturbing force 152 



70. Defect of this theory; sketch of Poisson's more complete 



theory ..*....... 154 



71. Inadmissibility of Poisson's fundamental suppositions, and 



indication of the wants of a new theory .... 156 



72. Complexity introduced, by induction, into the actions of 



magnets upon each other . . . . . . . 160 



