PABAMAONETIC AND DIAMAGNETIC FORCES 345 



netism and diamagnetism, remains to be stated. Prisms 

 of the same heavy glass as that with which the diamag- 

 netic force was discovered were substituted for the metal- 

 lic cylinders, and their action upon the magnet was proved 

 to be precisely the same in kind as that of the cylinders 

 of bismuth. The inquiry was also extended to other in- 

 sulators: to phosphorus, sulphur, nitre, calcareous spar, 

 statuary marble, with the same invariable result: each of 

 these substances was proved to be polar, the disposition 

 of the force being the same as that of bismuth and the 

 reverse of that of iron. When a bar of iron is set erect, 

 its lower end is known to be a north pole, and its upper 

 end a south pole, in virtue of the earth's induction. A 

 marble statue, on the contrary, has its feet a south pole, 

 and its head a north pole, and there is no doubt that the 

 same remark applies to its living archetype ; . each man 

 walking over the earth's surface is a true diamagnet, 

 with its poles the reverse of those of a mass of magnetic 

 matter of the same shape and position. 



An experiment of practical value, as affording a ready 

 estimate of the different conductive powers of two metals 

 for electricity, was exhibited in the lecture, for the pur- 

 pose of proving experimentally some of the statements 

 made in reference to this subject. A cube of bismuth was 

 suspended by a twisted string between the two poles of 

 an electro-magnet. The cube was attached by a short 

 copper wire to a little square pyramid, the base of which 

 was horizontal, and its sides formed of four small trian- 

 gular pieces of looking-glass. A beam of light was suf- 

 fered to fall upon this reflector, and as the reflector fol- 

 lowed the motion of the cube the images cast from its 

 sides followed each other in succession, each describing 



