16 Messrs. J. Tyndall and H. Knoblauch on the 



these particles are aggregated, the less will be the obstruction 

 offered to the transmission of the respective forces among 

 them? It is this closeness of arrangement in the cases just 

 cited, which gives to the iron and bismuth wire their predomi- 

 nance; for the interposed flour particles obstruct the forces in 

 all other directions. If, therefore, in a magnetic or diamagnetic 

 mass, two directions exist, in one of which the contact of the 

 particles is closer than in the other, may we not fairly con- 

 clude that the strongest exhibition of force will be in the for- 

 mer line, which therefore will signalize itself between the 

 poles, in a manner similar to the bismuth or iron wire? The 

 case seems analogous to that of good and bad conductors in 

 electricity. This fluid will not quit the good conductor to go 

 to the bad. The powder magazine is safe, because the fluid 

 prefers the iron rod to any other path. As regards magnet- 

 ism, different directions, through the same body, may represent 

 these good and bad conductors; the line of preference being 

 that of closest contact among the material "particles. 



If analogic proof be of any value, we have it here of the very 

 strongest description. For example : — bismuth is a brittle 

 metal and can readily be reduced to a fine powder in a mor- 

 tar. Let a teaspoonf ul of the powdered metal be wetted with 

 gum-water, kneaded into a paste, and made into a little roll, 

 say an inch long and a quarter of an inch across. Hung be- 

 tween the excited poles, it will set itself like a little bar of bis- 

 muth — equatorial, Place the roll, protected by bits of paste- 

 board, within the jaws of a vice, squeeze it flat, and suspend 

 the plate thus formed between the poles. On exciting the 

 magnet the plate will turn, with the energy of a magnetic sub- 

 stance, into the axial position, though its length may be ten 

 times its breadth. 



Pound a piece of carbonate of iron into a fine powder, and 

 form it into a roll in the manner described. Hung between 

 the excited poles, it will stand as an ordinary magnetic sub- 

 stance — axial. Squeeze it in the vice and suspend it edge- 

 ways, its position will be immediately reversed. On the de- 

 velopment of the magnetic force, the plate thus formed will 

 recoil from the poles, as if violently repelled, and take up the 

 equatorial position. 



We have here " approach " and " recession," but the cause 

 is evident. The line of closest contact is perpendicular in each 

 case to the surface of the plate — a consequence of the pressure 

 which the particles have undergone in this direction ; and 

 this perpendicular stands axial or equatorial according as the 

 plate is magnetic or diamagnetic. We have here a " a direc- 

 tive force/' but it is attraction or repulsion modified. May 



