10 



of convergence are uniform ; their focus of convergence being 

 equal to the transverse area of the magnetic axis at both ends. 



We find in measuring the force along the magnetic curves, 

 that it varies inversely as the distance ; allowing for the influence 

 of the earth's magnetism and tracing the effects in a horizontal 

 plane, we obtain the following law, viz. that the force varies in* 

 versely as the square of the distance from the surface of the ball 

 in the equatorial plane, and also in the meridian from the poles 

 towards the equator ; being the necessary consequences of the 

 expansion and compression of the magnetic fluid surrounding it, 

 as shown in the sketches. This is precisely the law of what is 

 called gravitation, but the meridional variation towards the poles 

 of the earth has been ascribed to the effect of a centrifugal force 

 produced by the earth's rotation. The assumed centrifugal effect 

 of the earth's rotation is also considered as the cause of the earth 

 being an oblate spheroid. In the first place, a globe constituted 

 and placed under similar conditions as our earth is, with its 

 enveloping fluids, placed under the influence of centripetal and 

 centrifugal forces alone, according to the well-known laws of 

 physics, would not, nor could not produce the observed figure, 

 much less the observed variation of attraction towards the poles. 

 Its magnetism alone, without rotation, must necessarily com- 

 press the poles, and also cause the inverse law of intensity in the 

 enveloping fluids. 



In order to show further, that there is no necessity for a rota- 

 tory or a centrifugal force to cause, or at least to preserve an 

 oblate spheroid in a similar body, let us take the moon for an 

 example. She is an oblate spheroid, yet she does not rotate, 

 i. e. on an axis situated within her body, because she always pre- 

 sents the same face towards the earth. Had the earth continued to 

 present the same face towards the centre of its orbit, it could not 

 rotate, yet we find a body similarly situated an oblate spheroid. 



To return to our subject : we find that magnetism alone tends 

 to form a sphere into an oblate figure, by the variable intensity 

 of the currents on its surface, and that this effect is observed 

 on our globe. If this be the primary agent by which all the 

 substances of our globe are governed, we ought to be able to 

 trace its effects according to the above principles of action, viz. 

 circulating from south to north over the surface of our earth, 



