482 On Mental Education. [1855. 



joining the poles ; when only one pole is near the bar, the latter 

 recedes ; this and the former effect are due to repulsion, and are 

 strikingly in contrast with the attraction shown by iron. To 

 account for it, I at one time suggested the idea that a polarity 

 was induced in the phosphorus or bismuth the reverse of the 

 polarity induced in iron, and that opinion is still sustained by 

 eminent philosophers. But observe a necessary result of such 

 a supposition, which appears to follow when the phenomena 

 are referred to elementary principles. Time is shown, by every 

 result bearing on the subject, to be concerned in the coming on 

 and passing away of the inductive condition produced by mag- 

 netic force, and the consequence, as Thomson pointed out, is, 

 that if a ball of bismuth could be suspended between the poles 

 of a magnet, so as to encounter no resistance from the surround- 

 ing medium, or from friction or torsion, and were once put in 

 motion round a vertical axis, it would, because of the assumed 

 polar state, go on for ever revolving, the parts which at any 

 moment are axial moving like the bar, so as to become the next 

 moment equatorial. Now, as we believe the mechanical forces 

 of nature tend to bring things into a stable, and not into an 

 unstable condition ; as we believe that a perpetual motion is 

 impossible ; so because both those points are involved in the 

 notion of the reverse polarity, which itself is not supposed to 

 be dependent on any consumption of power, I feel bound to 

 hold the judgment balanced, and therefore hesitate to accept 

 a conclusion founded on such a notion of the physical action ; 

 the more especially as the peculiar test facts* which prove the 

 polarity of iron are not reproduced in the case of diamagnetic 

 bodies. 



As a result of this wholesome mental condition, we should 

 be able to form a proportionate judgment. The mind naturally 

 desires to settle upon one thing or another; to rest upon an 

 affirmative or a negative ; and that with a degree of absolutism 

 which is irrational and improper. In drawing a conclusion, it 

 is very difficult, but not the less necessary, to make it propor- 

 tionate to the evidence : except where certainty exists (a case 

 of rare occurrence), we should consider our decisions as pro- 

 bable only. The probability may appear very great, so that in 

 affairs of the world we often accept such as certainty, and trust 

 * Experimental Researches in Electricity, paragraphs 2G57-2681. 



