298 Dr. Faraday's Researches in Electricity. [Series xix. 



trary direction to what it was before ; and when the magnetic 



pole was changed, both these directions were changed with it. 



When the heavy glass was placed in a corresponding position 



to the pole, but above or below it, so that the magnetic curves 



were no longer passing through the glass parallel to the ray 



of polarized light, but rather perpendicular to it, then no effect 



was produced. These particularities may be understood by 



reference to fig. 1, where a and b represent the first positions 



of the diamagnetic, and c and d the 



latter positions, the course of the 



ray being marked by the dotted 



line. If also the glass were placed 



directly at the end of the magnet, 



then no effect was produced on a 



ray passing in the direction here 



described, though it is evident, 



from what has been already said 



(2155.), that a ray passing parallel 



to the magnetic lines through the 



glass so placed, would have been affected by it. 



2160. Magnetic lines, then, in passing through silicated 

 borate of lead, and a great number of other substances (21 73.), 

 cause these bodies to act upon a polarized ray of light when 

 the lines are parallel to the ray, or in proportion as they are 

 parallel to it: if they are perpendicular to the ray, they have 

 no action upon it. They give the diamagnetic the power of 

 rotating the ray; and the law of this action on light is, that if 

 a magnetic line of force be going from a north pole, or coming 

 from a south pole, along the path of a polarized ray coming 

 to the observer, it will rotate that ray to the right-hand; or, 

 that if such a line of force be coming from a north pole, or 

 going from a south pole, it will rotate such a ray to the left- 

 hand. 



2161. If a cork or a cylinder of glass, representing the dia- 

 magnetic, be marked at its ends with the letters N and S, to 

 represent the poles of a magnet, the line 

 joining these letters may be considered as a 

 magnetic line of force; and further, if a line 

 be traced round the cylinder with arrow 

 heads on it to represent direction, as in the 

 figure, such a simple model, held up before 

 the eye, will express the whole of the law, 

 and give every position and consequence of 

 direction resulting from it. If a watch be considered as the 

 diamagnetic, the north pole of a magnet being imagined 



