366 FRAGMENTS OF SCIENCE. 



earth. It has already been stated that the softest iron 

 possesses a certain amount of coercive force. The 

 earth, at this moment, finds in this force an antagonist 

 which opposes the decomposition of the neutral fluid. 

 The component fluids may be figured as meeting an 

 amount of friction, or possessing an amount of ad- 

 hesion, which prevents them from gliding over the 

 molecules of the poker. Can we assist the earth in this 

 case? If we wish to remove the residue of a powder 

 from the interior surface of a glass to which the powder 

 clings, we invert the glass, tap it, loosen the hold of 

 the powder, and thus enable the force of gravity to pull 

 it down. So also by tapping the end of the poker we 

 loosen the adhesion of the magnetic fluids to the mole- 

 cules and enable the earth to pull them apart. But, 

 what is the consequence? The portion of fluid which 

 has been thus forcibly dragged over the molecules 

 refuses to return when the poker has been removed 

 from the line of dip; the iron, as you see, has become 

 a permanent magnet. By reversing its position and 

 tapping it again we reverse its magnetism. A thought- 

 ful and competent teacher will know how to place 

 these remarkable facts before his pupils in a manner 

 which will excite their interest. By the use of sensible 

 images, more or less gross, he will first give those whom 

 he teaches definite conceptions, purifying these con- 

 ceptions afterwards, as the minds of his pupils become 

 more capable of abstraction. By thus giving them a 

 distinct substratum for their reasonings, he will con- 

 fer upon his pupils a profit and a joy which the mere 

 exhibition of facts without principles, or the appeal to 

 the bodily senses and the power of memory alone, could 

 never inspire. 



