1069 
of the dimensions of the magnet that was used, therefore of the 
demagnetising force proved to be great. So AsnwortH found e.g. for 
one single piano-string of certain dimensions a negative value of «, 
while three equal and equally treated strings combined into a bundle 
gave a positive value of «. 
In the experiments that are to be described here, iron and further 
also some kinds of steel were used. 
The iron (soft Swedish iron from G. E. Mristrr’s SönNe, Stettin) 
was investigated in the form both of bars and of a ring. In the 
first case the measurements were magnetometric, in the latter one 
ballistic. For the magnetometric measurement a THOMSON galvanometer 
was used. The magnet that had to be investigated was placed 
horizontal and perpendicular to the direction of the small magnets 
in the galvanometer system. The deviation of the system by the 
presence of the magnet was compensated by sending a current through 
the coils. The intensity of this current was used as a measure for 
the magnetic force that was exerted by the magnet. In order to 
avoid the influence of terrestrial magnetism the bar was always 
placed perpendicular to the magnetic meredian. 
The ballistic measurements were made by means of a flat coil 
that could be brought into the interferricum of the ring. 
For the different forms used the demagnetising factors were very 
unequal. They had the highest value for a bundle of bars with total 
diameter of about i.5 em and 24 cm length; and the lowest one 
for the torus with narrow interferricum. The magnetisation was also 
varied within rather wide limits. The mentioned bundle gave for a 
variation of temperature between 10° and 100° and for magne- 
tisations that were in the ratio 1: 2:12 changes resp. of 3.7, 3,8 
and 3,7°/,. Between the same limits of temperature a bar of 0,5 em 
diameter and 21 em length gave a change of 4,0°/, and one of 
0,3 em diameter and 17 em length of 4,1°/,. In the two last cases 
the magnetisation was nearly as strong as the strongest magnetisation 
in the case of a bundle of bars. In all cases the magnetisation did 
not reach its saturation value, though the strongest magnetisation 
did not differ much from it. For the ring made of iron of 23 mm 
diameter and having itself a diameter of about 10 em with an inter- 
ferricum of 2 mm a variation of 4°/, was obtained for weak 
magnetisations between 20° and 100°. 
So the values for the variations of temperature obtained for iron 
do not differ much from each other. It is questionable, whether 
these differences have a real significance; probably they must be 
assigned to observation errors, as the methods used did not allow 
