178 Dr. Tyndall on Diamagnetism and Magnecrystallic Action, 



large crystals were obtained from a chemical manufactory, and 

 from these I cut two clean cubes. Each was suspended by a 

 cocoon fibre in the magnetic field, and the line which stood axial 

 was marked upon it. The white powder which collects by ef- 

 floresence around these crystals was washed away, and two 

 transparent cubes remained. These were laid upon the torsion- 

 balance, and instead of the Bristol board two plates of glass were 

 placed against the core ends ; the adhesion of the cubes, which 

 in delicate experiments of this nature sometimes enters as a dis- 

 turbing element, was thus reduced to a minimum. As in the 

 case of carbonate of iron, one core only was excited. The cube 

 opposite to this core was first so placed that the line which stood 

 axial in the magnetic field was parallel to the core ; preserving 

 this line horizontal, the three remaining faces were presented 

 successively to the core and the attraction measured in each par- 

 ticular case j these attractions were as follows : — 



Cube of sulphate of iron j edges 10 millims. 



Attraction. 



1st position 43-0 



2nd position 36'3 



3rd position 40*0 



4th position 34*5 



Hence the attraction of this crystal in the direction of the 

 line which sets axial in the magnetic field, is to the attraction in 

 a direction perpendicular to the same in the ratio of 7 : 6 nearly. 



In an article translated from Poggendorf^s Annalen, which 

 appears in the June Number of the Philosophical Magazine, it will 

 be seen that Prof. Pliicker has experimented with a cube of sul- 

 phate of iron, and has arrived at results which he adduces against 

 the theory of magnecrystallic action advanced by Knoblauch 

 and myself. He rightly concluded that if the position of the 

 crystal, suspended between two poles, were due to the superior 

 attraction exerted in a certain direction, this peculiarity ought 

 to exhibit itself in the attraction of the entire mass of the crystal 

 by the single pole of a magnet. He brings this conclusion to 

 the test of experiment, suspends the ci-ystal from one end of a 

 balance, weighs the attraction in different directions, but finds 

 no such difi*erence as that implied by the conclusion. This re- 

 sult I believe is entirely due to the imperfection of his apparatus j 

 I have tried a very fine balance with even worse success than 

 M. Pliicker. Although the torsion-balance furnishes a means 

 of experiment immeasurably finer, still, with it, great delicacy of 

 manipulation and a considerable exercise of patience are neces- 

 sary to ensure invariable success. It is gratifying to find M. 

 PlUcker's deduction so strictly fulfilled, and I doubt not that he 



