ÈEÏWÈEN LOXGIÏUDIXAL AXD CIKCULAK MAGx\ETIZATIONÖ. 285 



layers with copper wire of 1 mm. diameter, and gave tlie field 

 of 29.5 C.G.S. iuiit8 at the middle of the coil due to tlie cur- 

 rent of one ampère. The internal diameter of the coil was 2.7 

 cm. and the external oA cm. It was ])laced in horizontal posi- 

 tion with its axis perpendicular to the magnetic meridian. 



The strength of the magnetizing current was measured by 

 Thomson graded galvanometer which was carefully compared 

 with deciampère balance both before and after each experiment. 



The ballistic galvanometer was of Wiedemann form, Avith cop- 

 per damping. Its resistance was about 52 ohms, and its period of 

 vibration was about 6 seconds. It was 4 m. distant from the 

 magnetizing coil. The constant of the galvanometer was deter- 

 mined by means of a standard coil which was always placed in 

 the secondary circuit. The last mentioned coil was Avound in a 

 single layer with fine copper wire on a glass tube, whose diameter 

 was 2.724 cm. and had ÖOO turns. It was placed in another 

 coil whose field at the centre due to the current of one ampère 

 was î>6.0 C.G.S. units, and the constant of the galvanometer was 

 determined by the ballistic throw at the make and break of the 

 current in the primary coil. 



The ferromagnetics used in the present investigation had the 

 following dimensions : — 



1. Wire of Swedish iron : 



length^ 21.00 cm.; diameter = 1.34 mm.; demagnetizing 

 factor =0.0011). 



2. Tube of Swedish iron : 



lengtli = 20.70 cm.; external diam. =0.416 ; internal diam. 

 =0.335 cm.; demagnetizing factor =0,0063. 



3. Tube of soft iron : 



lengtli = 16.7*J cm.; external diam. =0.966 cm.; internal 



