INTENSITY OF MAGNETIC AND DIAMAGNETIC FORCES, 739 



rection, and this not so much on account of the method adopted 

 in their determination, as on account of the uncertainty regarding 

 the chemical purity of the substances, to which point in subse- 

 quent determinations of this kind attention should be principally 

 directed. 



§ 3. Comparison of the Intensity of the Diamagnetism of different 

 substances. 



38. I shall next detail the results of two series of experiments, 

 which were performed by the method developed at the end of 

 the 6th paragraph. The electro-magnetism was in both cases 

 excited by a battery of ten Grove's cells ; and in each case nitric 

 acid, which had not been previously used, and a mixture of 

 1 part of sulphuric acid and 12 parts of water (by volume) were 

 taken. The watch-glass, with its ground cover, was filled with the 

 various substances in succession ; and when thus filled, was ex- 

 posed, as described in the 5th paragraph, to the two halves of the 

 keeper, the rounded ends of which were turned towards each 

 other, so that it touched each of them at a single point only. 

 In the determination of the attraction of the watch-glass which 

 then ensued, the error of observation certainly did not amount 

 to 0*01 grm. The weight of the solid bodies was determined in 

 each case, and usually the specific gravity of the fluids was sub- 

 sequently taken. 



In the first series of experiments the following results were 

 obtained : — 



|g grm. 



■ Attraction of the empty watch-glass with itsl^^ .„ 



1 h • '>•. 



cover and brass ring J 



Attraction of the watch-glass filled with — 



1. Distilled water 0-35 



2. Alcohol 1 0-36 



3. Sulphuric cether 0-36 



4. Solution of ferrocyanide of potassium . . 0*37 



5. Solution of ferridcyanide of potassium . . 0*72 



6. Phosphorus 0-245 



7. Oxide of bismuth 0-43 



8. Flowers of sulphur 0-39 



9. Sulphuric acid 0'40 



39. To test the constancy of the force of the magnet, weighings 

 of a second watch-glass, already mentioned in paragraph II, and 



