178 Professor TyndalPs further Researches 



Comparing these deflections with those obtained with diamag- 

 netic bodies, we see that they are in the opposite direction. 

 With the direct current a change from position 1 to 3 is fol- 

 lowed, in the case of diamagnetic bodies, by a motion from 

 higher to lower numbers ; while in the present instance the 

 motion is from lower numbers to higher. In the former case 

 the north poles of the astatic magnet are attracted, in the latter 

 they are repelled. We also see that a direct current acting on 

 diamagnetic bodies produces the same deflection as a reverse cur- 

 rent on magnetic ones. Thus, as we promised at a former 

 page, the opposite polarities of diamagnetic and magnetic bodies 

 are transferred from the region of deduction to that of fact. 



XIX. 



Cylinder of Caermarthen Slate. 

 Length 4 inches. Diameter 0'7. 



The deflections in this case are also indicative of magnetic po- 

 larity. 



These two cylinders were so taken from the rock that the axis of 

 each lay in the plane of cleavage. The following experiments, 

 made with a cylinder of the same size, show the capability of a 

 rock of this structure to be magnetized across the planes of 

 cleavage. 



XX. 



Cylinder of Slate : axis of cylinder perpendicular to cleavage. 



Current direct. Current reversed. 

 Position 1. 655 240 



Position 2. 678 205 



Position 3. 695 192 



Chloride of iron was next examined : the substance, in powder, 

 was enclosed in a single glass tube, which was attached to the 

 string passing round the wheels WW' of the instrument. 



XXI. 



Cylinder of Chloride of Iron. 



Length 3*8 inches. Diameter 0*5. 



Current direct. Current reversed. 



Position 1. 185 990 



Position 2. — 230 



Position 3. 990 185 



