produced by Magnetization. 461 



this, 1 made use of the method described by Bottger* to obtain 

 by the electrolytic process a coherent precipitate of iron, — but 

 with this difference, that the precipitation was conducted between 

 the poles of a powerful magnet. A cylindrical glass vessel was 

 divided by means of a porous partition into two cells, each of 

 which contained a solution of iron (sulphate or chloride with 

 sal-ammoniac). In one cell a steel plate was plunged perpen- 

 dicularly as the positive pole, in the other, parallel to the first, a 

 rectangular strip of plated metal of any kind as negative pole. 

 The longer side of the latter was horizontal, the shorter side 

 touched the side of the vessel. A strong magnet (sometimes a 

 magnet of seven plates and 50 lbs. attractive power, sometimes 

 a Logemann's magnet of 25 lbs. attractive power) was placed 

 horizontally on the table, so that the glass tube projected partly 

 between its limbs, and the inner polar edge of the magnet 

 touched the outside of the glass vessel exactly where the 

 negative plate lay against it on the inside. A simple DanielFs 

 battery served as electromotor. 



The iron plates thus obtained were hard as glass, and always 

 magnetic. In fact, however, so strong a magnetic influence was 

 by no means necessary to render them permanently polar; on 

 the contrary, almost any magnetic force operating during the 

 formation of the precipitate, was sufficient to determine its 

 polarity. Every electrolytic iron plate, for example, is magnetic 

 if the cathode has been placed in the direction of the magnetic 

 inclination. 



In order to test the power of the magnets thus obtained, they 

 were placed on edge near a mirror magnetometer, so that their 

 axis passed through the axis of rotation of the mirror, and lay 

 magnetically east and west. Then, to measure the temporary 

 magnetism and the changes produced in it by magnetizing 

 currents, this whole arrangement was placed within one of the 

 large magnetizing coils taken from a Kleiner's electromagnet. 

 As, however, the magnetism produced by such a coil, even when 

 weak currents were employed, turned the mirror through so 

 great an angle that the graduated scale passed entirely out of 

 the field of vision of the telescope, the other coil was placed near 

 the magnetometer on the other side, and the current was made 

 to pass through both in succession, under which circumstances 

 the deviation of the electrometer only amounted to a few divisions 

 of the scale. The natural position of the mirror of the magneto- 

 meter was then observed, and its positions noted when a current 

 was made to pass through the coil, first in one direction, then 

 in another; the bar magnet under examination was then inserted 



* Polyt. Notizbl. vol. i. No. 4. p. 849. Pogg. Ann. vol. lxvii. p. 117. 

 Dingl. Pol, Joum. vol. xcix. p. 296. 



