16 Barrerr, Brown, & Haprimnp—On the Magnetic and Electric 
annexed curves, fig. 6, were drawn. Here the ordinates represent the permeability 
(B/H) instead of B, the abscissee being magnetising forces as before. 
These curves show that the aluminium-iron attains its maximum per- 
meability in a field of about 0°5 unit, when 
it reaches the unprecedented value of 9000; 
the silicon-iron alloy has its maximum of 
6400 in a field of 1 unit; and the Swedish 
charcoal-iron its maximum of about 4000 in a 
field of 1:5 unit. In fact, so magnetically soft 
are these alloys of aluminium- and silicon-iron, 
especially the former, that the vertical component 
of the Earth’s magnetic force (equal 0-46 C.G.S. 
in Dublin) magnetises these alloys strongly when 
they are held vertically. Still more remarkable 
is the fact that, notwithstanding their length 
is 260 diameters, the mere reversal of the 
rods, without any jar or shake, instantly and CA 
completely reverses the magnetic polarity of hie 
the aluminium-iron and nearly reverses the |. oe ee ee Bh 
silicon-iron, but only very partially reverses nt fields of/aluminium. and silicon-iron alloys 
2 i é compared with Swedish charcoal-iron. 
the pure soft iron 8. C. I. which required 
slight tapping before complete magnetic reversal took place. This is shown 
by the accompanying table when the rods are compared under identical 
Permeability 
ane 
ma 
| 
Lio 
a 
Pi 
NEILL 
LI 
NO 
SS 
[) 
nea 
aay 
conditions. 
TABLE X. 
MAGNnEroMETRIC DreFLECTIONS PRODUCED By THE Harry’s Magneric FIELD oN 
SLENDER RODS OF— 
Swedish Charcoal-Iron 85, when rod reversed 15. 
Silicon-Iron Alloy 68, Sos - 58. 
Aluminium-Iron Alloy 90, an Biss 3 90. 
Here the rods were, each in succession, held vertically at exactly the 
same distance from the reflecting magnetometer: the magnetometric deflections 
due to the Earth’s magnetising force, are given in the second column ; these being 
proportional to the tangents of the respective angles, therefore measure the relative 
permeability of the three rods in a magnetic field of about 0°5 C. G.S. unit. When 
the rods were carefully reversed without the least shock, so that the lower end 
occupied the precise position formerly held by the upper end, the deflections 
produced were in the same direction as before, showing the reversal of the 
magnetisation of the rods. | 
Aiter the experiments, to be subsequently described, had been made, the 
