36 Wm. A. Norton on the Variations 



of matter at the earth's surface, and to a certain depth below the 

 surface, is the centre of a magnetic force exerted tangentially to 

 the circumference of every vertical circle that may be conceived 

 to be traced around it. 2. The direction of this force is different, 

 according as it solicits the north or south end of the needle; and 

 it is always such, that to the north of the acting particle the ten- 

 dency is to urge the north end of the needle downward and the 

 south end upward, and that to the south of the same particle it 

 is to urge the north end upward and the south end downward. 

 3. The intensity of the magnetic force of a particle of the earth, 

 at a given distance, is approximately proportional to its tempera- 

 ture, or amount of sensible heat ; and at increasing distances, 

 diminishes according to some unknown law. I was conducted 

 to these principles by the theory which I had been led to adopt 

 concerning the physical nature of the Imponderables ; which is, 

 that all the phenomena of the imponderables are but different 

 effects of different vibratory motions of the particles of matter, 

 and of the ethereal undulations produced by these vibrations. I 

 accordingly conceived each particle of the earth's mass to be the 

 centre of a system of undulatory movements propagated through 

 the surrounding ether, and of every variety of time and intensity 

 of vibration within certain limits — waves of light, heat, and 

 magnetism. The vibrations of the ethereal particles, in a wave 

 of magnetism, I supposed to be in the surface of the wave, or 

 transversal to the line of propagation of the wave, as is known 

 to be the case with a wave of light, and I regard the magnetic 

 forces as probably due to these transversal vibrations. I was thus 

 led to consider the sun as the probable source, at the same time, 

 of waves of heat, light, and magnetism, and that the molecular 

 forces of vibration due to the different kinds of waves would 

 probably vary according to the same law, or approximately so, 

 in passing from one point to another on the earth's surface, and 

 accordingly that the temperature of a particle might be taken as 

 a measure of its magnetic force. Although I was thus conduct- 

 ed, by these physical speculations, to the fundamental principles 

 of what may be characterized as the Thermal Theory of Ter- 

 restrial Magnetism, these principles may nevertheless have no real 

 connection with the physical theory in which they originated. 

 The tangential magnetic forces which I suppose, may be due to 

 electric currents or may be fundamental properties of matter. 

 The investigations of this and the previous memoir, conclusively 

 establish the fact of the existence of these forces, and of their 

 supposed connection with the thermal state of the earth, but are 

 in no way essentially dependent upon any physical speculations 

 concerning their origin. These form a debatable ground beyond 

 the thermal theory which I have undertaken to develop and fol- 

 low out into some of its consequences, about which I do not at 

 present concern myself. 



