164 



Prof. G. Wiedemann on the Magnetic 



means of a horizontal endless screw gearing into its edge and 

 turned by a cord led to the observer. To the head was sus- 

 pended, by a very hard-drawn German-silver wire of 0* 2-0-3 

 millim. thickness, and 640 millims. length, a vertical brass 

 rod. A, 550 millims. long and 5-5 millims. thick, loaded beneath 

 with weights (about a kilogram), and furnished at its lower 

 extremity with vanes which were immersed in a glass vessel n, 

 filled with oil, in order to damp the oscillations of the appa- 

 ratus. On the brass rod, 

 about 70 millims. below 

 its upper end, a hori- 

 zontal arm, ^, 20 mil- 

 lims. long, was fastened, 

 filed outquadrangularly 

 in front, so that exact- 

 ly fitting quadrangular 

 brass rods could be in- 

 serted in it, which sup- 

 ported in a brass holder 

 little flask-shaped glass 

 vessels, k, balanced by 

 a counterpoise. The 

 glass vessels were partly 

 spherical, partly flat- 

 tened, so that their 

 plane surfaces were pa- 

 rallel with the vertical 

 plane pasing through the bniss rod and the arm. These ves- 

 sels were filled, up to a mark on tlie neck, with the substances 

 to be investigated. In the position of rest the arm i was in 

 the magnetic north-and-south plane. In front of the glass 

 vessel k a very powerful electromagnet, Z, was placed in an 

 east-and-west position : in the more recent experiments it con- 

 sisted of an iron core terminating in front in a truncated cone, 

 of 320 millims. length and 70 millims. diameter, placed in a 

 helix of 1200 turns of covered copper wire 2*5 millims. in 

 thickness. Its magnetic moment, J, was determined, by 

 means of scale and telescope, from the deflections of a steel 

 magnetic needle suspended in a thick copper box, set up in 

 the direction of the prolongation of the axis of the magnet, at 

 a distance of 230 centims. from its fore end. 



A mirror, g, fixed to the brass rod h, permits the orientation 

 of the apparatus to be observed by means of a scale at the dis- 

 tance of 2 metres and a telescope. First its 7iz7-position was 

 determined without the magnet's influence ; then the magnet 

 was excited, its moment, J, dctennined, and by turning the 



