Dr. Tyndall on Diamagnetism and Magnecrystallic Action. 169 



commencing a series of experiments,, the little beam was proved. 

 With very strong currents it was found to be slightly diamag- 



Ficf.2. 



neticj but so feeble^ that its action, even supposing it not to 

 follow the same law of increase as the ball (which, however, it 

 certainly does), could cause no measurable disturbance. 



I neglected no precaution to secure the perfect purity of the 

 substances examined. The entire investigation was conducted 

 in the private cabinet of Professor Magnus in Berlin ; and at the 

 same time a gentleman. Dr. Schneider, happened to be engaged 

 in the Professor^s laboratory in determining the chemical equiva- 

 lent of bismuth. From him I obtained a portion of this sub- 

 stance prepared in the following way : — The metal of commerce 

 was dissolved in nitric acid and precipitated with distilled water ; 

 whatever iron was present remained in the solution. The preci- 

 pitate was filtered, washed for six days successively, and after- 

 wards reduced by means of black flux. The metal thus obtained 

 w^as again melted in a Hessian crucible, and saltpetre was gra- 

 dually added, the mass at the same time being briskly stirred. 

 Every remaining trace of foreign ingredient was thus oxidized 

 and rose to the surface, from which it was carefully skimmed. 

 The metal thus purified was cast into a bullet-mould, the interior 

 surface of which was coated by a thin layer of oil ; the outer sur- 

 face of each bullet was carefully scraped away with glass, the 

 ball was then scoured with sea-sand, and finally boiled in hydro- 

 chloric acid. I have already described the method of experiment. 

 The bismuth balls were placed upon the hollows of the beam, 

 and their repulsions by various currents determined in the manner 

 indicated. The series of repulsions thus obtained are exactly 



