SCIENTIFIC SUMMARY. 
103 
successively increasing temperatures from 100° up to 310°. The heated oil 
was used also to temper a number of parcels by plunging them at a bright 
red heat into the oil at various temperatures. 
All the bars were then magnetised by the current from ten Tray Daniells 
passing through a coil the same length as the bars, containing four layers of 
forty turns each, or 160 turns in all. The magnetising force was calculated 
at 377. 
The value of the horizontal component of the earth’s magnetic force at 
the place was computed by observing the period of oscillation of five 
separate magnets in reversed positions. The mean result, without correction 
for induction, was T5399. 
The magnets originally named were then magnetised a second time by a 
double battery and a coil of ten layers and seventy turns, giving a magn etis- 
ing force of 1100. To show the relative effects of different magnetising forces 
on bars tempered “ glass-hard ” and “ blue,” two bars were brought, one to 
each of these tempers, and then magnetised, first with very small magnetising 
force, increased by measured amounts. The results are given in two compared 
curves, of which abscissae are proportional to magnetising force, and ordinates 
to magnetic moments. The blue magnet is seen to rise more rapidly and to a 
higher point of saturation, though from 300 to 1,000 of abscissae the two run 
near together and all but parallel, the blue slightly above the “ glass-hard.” 
Magnets made of steel, suddenly cooled in cold water, were scarcely so 
strong as those which had afterwards been heated in oil up to 310° O., 
and allowed to cool slowly. By a second and stronger magnetisation, this 
difference was much diminished, probably from the softer steel being more 
easily raised to saturation. Bars cooled in cold oil had small magnetic 
moment; but this factor increased as the oil was raised to 150° O. It then 
amounted to 60 to 80 per gramme weight. 
Homogeneous iron, or “mild steel,” was also experimented on. In a 
“ glass-hard” condition its magnetic moment was only 20-22, and at a blue 
temper little more than half this. 
As regards permanence of the magnetism, it was little changed by nine 
months’ undisturbed quiescence. The hard magnets lost about 2 per cent, of 
their moment when allowed to fall three times, with true north pole, down 
from a height of 70 centim. on a hard paving-stone. Blue magnets lost 
10 per cent. After nine months the hard lost 0-5, and the blue 2-8, by the 
same treatment. The essay concludes with a series of tables embodying 
the above facts in a numerical form. 
Binaural Audition . — The principal conclusions which Professor S. P. 
Thompson comes to on this subject are: — 
(1.) There is interference in the perception of sound; for two simple 
tones capable of interfering are still heard to interfere when conducted 
separately to the two ears. 
(2.) When two simple tones in unison reach the ears in opposite phases, 
the sound is localised at the back of the head. 
(3.) The localisation of this acoustic “image” is independent of the pitch 
of the sounds. 
(4.) When the difference of phase is partial, the] sensation is localised, 
partly in the ears, and partly at the back of the head. 
