568 PLUCKER ON THE ACTION OF THE MAGNET 



the surfaces of the poles ; and in consequence their surface 

 assumes remai'kable forms, the perfect explanation of which we 

 find in the analogous appearance from which we started in this 

 paragraph. I shall next describe these phaenomena as they 

 occur in a powerfully magnetic liquid, a tolerably concentrated 

 aqueous solution of per chloride of iron, 



34. I chose the halves of the keeper (C), mentioned in the 

 second paragraph, on account of their greater size, and applied 

 them, with the polished grooves downwards, to the surfaces of the 

 poles of the electro-magnet in such a manner that the rounded 

 ends were turned towards each other, and retained at a definite 

 distance apart. A watch-glass cut from a sphere, the radius of 

 which was 36 millims., was so placed upon the halves of the 

 keeper as to be in contact with them at those points which were 

 nearest each other, and the liquid was then put into it. When 

 the least distance apart of the two halves of the keeper amounted 

 to 2'5 millims., and when the quantity of the liquid was such 

 that its circumference formed a circle of 35 millims. in diameter, 

 on closing the circuit the liquid assumed such a form as, when 

 seen from above, to appear bounded by an almost true geome- 

 trical ellipse, the large axis of which was in the equatorial plane 

 and the small axis in the perpendicular meridional plane of the 

 magnet*. The former was 40 millims. and the latter 25 mil- 

 lims. in length. The height of the liquid, before and after the 

 closing of the circuit, was measured by the spherometer, and it 

 was thus proved that the magnetic force had raised the fluid in 

 the centre 1*12 millim. In fig. 8 the larger circle represents the 

 original boundary of the liquid viewed from above, and this 

 circle is changed by the magnetic action into the outer ellipse. 

 The liquid is forced into the equatorial plane, forming in it an 

 elevated ridge, the crest of which is constituted by a curve, 

 which in the middle almost slopes off to a straight line, and at 

 the ends, its convexity being altered, rapidly sinks down to the 

 glass. The section in the meridional plane is bounded above by 

 a curve elevated in the middle. 



♦ By this term, in conformity with Faraday's system of notation, I denote 

 all planes passing through the axial (that uniting the poles) right line. When 

 any two symmetrical halves of the keeper are applied to the surfaces of the poles 

 of a horseshoe magnet, there are always two principal planes, one of which 

 passes through the axes of the two arms ; the second, wliich is perpendicular to 

 the first, through the central line of the magnet. Hereafter we shall deiiomi' 

 nate the former the meridional, and the second the equatorial plane. 



