Dr. de Haldat on the Universality of Magnetism. 321 



gum, bees wax, &c. ; we may also add gold obtained from 

 deposit, silver reduced from the chloride, and copper preci- 

 pitated by galvanism. Each of these substances was placed 

 upon a sheet of very thin paper, previously purified and 

 suspended by a double filament of silk, and submitted to the 

 influence of the two poles of a horse-shoe iron magnet car- 

 rying twenty-five kilogrammes. With respect to their be- 

 haviour under the influence of this double power, they are 

 divided into two classes, conformably to the observation of 

 Mr. Faraday, previously recognised by M. Becquerel*. One 

 class was placed in the direction of the magnetic current, the 

 other transversely to this current. There is therefore no sub- 

 stance absolutely neutral with regard to the property of 

 acquiring the magnetic power; but whatever be the direction 

 which it takes, this can always be ascertained, and the acquired 

 power determined, even measured, by means of the parts of 

 the apparatus which measures the torsion. 



Reverting to the question of the universality of magnetism 

 and the speciality of the iron which it repels, the author has 

 discussed the objections raised against the distinction of the 

 two modes of magnetization, which, with the fact of the pola- 

 rization of the luminous ray under the influence of the mag- 

 netic current, has strongly confirmed a theory already based 

 on so many remarkable analogies and numerous experiments. 

 He has refuted the fact of the variations in the direction of 

 needles successively reduced to disproportionate lengths, which 

 have been assigned to them from the consideration of the 

 powerlessness of the most energetic magnets to act otherwise 

 than upon the centre of the needles, and consequendy to give 

 them other than a transverse direction. 



In rejecting the magnetic speciality of iron, the author has 

 not denied the very remarkable pre-eminence of this metal 

 with regard to the property of acquiring the magnetic power, 

 which it always manifests with great energy, even when it only 

 exists in an excessively small mass. An entire article is de- 

 voted to the valuation of the variations of which this arrange- 

 ment is susceptible by the combination of oxygen, of several 

 other substances, and above all by the passage of the metal to 

 the saline state in which it is generally diamagnetic, even when 

 the components of the salt are only united by a weak afiinity. 

 In this examination it has been found, that a quantity of iron 

 inappreciable by the most delicate balance might be detected 

 by the magnetic process, and even estimated approximately; 

 that, however, this power diminishing with the quantity of the 

 metal which puts it in play, it necessarily finds its limit in the 



• Aunalcs dc Chimw ct de Plii/i'iquc, 2nd series, t. xxxvi. p. 337. 

 Phil, Mag. S. 3. Vol. 30, No. 202. May 1 8 17. Z 



