( 233 ) 
increased considerably during the experiments. Though the resistance 
in the circuit of the HArr-current was measured several times during 
the experiments, some of the interpolated values may still contain 
a small percentage error. In future I intend to avoid this by altering 
the construction of the plate carrier. 
4. Magnetic increase of resistance and crystallographic direction. 
The experiments made before on this subject with one of the 
bars (N°. 1) cut out of a crystalline piece from Merck ') have now 
been repeated at — 90° C. The method of observation was the same 
as described in Comm. NO. 48.*) The use of the above described 
vacuum-glass offered especial advantage in this case, for the bar 
could be rotated, together with the whole frame in which it was 
placed, about its greatest axis, which was vertical. In this 
manner the lines of magnetic force could be made to coincide with 
different crystallographic directions, without altering anything in the 
adjustment of the electrodes etc. This easy turning had only one 
disadvantage, that it sometimes occasioned movements during the 
experiments. For accurate measurements therefore it will be necessary 
to fix to the frame a rigid stem provided with an index. 
The foliowing results are therefore only mentioned because they 
evidently prove that the differences in increase of resistance formerly 
observed in different positions of the bar were only caused by the 
change of the angle between the lines of force and the crystallo- 
graphic directions. 
In the following table column I contains the positions in which 
the direction of maximum resistance *) coincided with the lines of 
force, I] the positions in which this direction was perpendicular 
to the lines of force. 
Percentage increase of resistance. 
Temp. MAGNETIC FORCE. 
2650 3800 
all IL 
2,2 5,8 
290° BENN A 4.38 okey 
| 1,3 3,2 
1) Versl. 21 April °97, p. 498. Comm. N°. 37, p. 13. 
2) Versl. 25 Maart ’99, p. 486. Comm. N°, 48, p. 6, 
*) Versl. 21 April '97, p. 498. Comm, N° 37. p. 13. 
