1904 - 5 .] Magnetic Quality in Molecular Assemblages. 1027 
Finally, it is assumed that the dimensions of the molecidar magnets 
are of such size in comparison with their average distance apart, 
that the fourth and higher powers of that ratio can he neglected. 
3. Weiss’s Experime7ital Results . — An extended series of observa- 
tions has been made, by P. Weiss, upon the magnetic properties 
of magnetite. His results were given in full in his thesis (Paris, 
Ho. 890, 1896), and in V itclairage electrique , 1896. A resume was 
also given in the Journal de Physique , 1896. I have only been 
able to obtain the latter account. The thesis is now out of print. 
Figs. 1-4, taken from the resume, show the main results. 
In fig. 1 the abscissae represent external field, while the ordinates 
represent magnetisation. The observations were made upon bars 
cut from the crystal in various directions, and special care was 
taken to avoid self-demagnetisation. The field varied from zero to 
500 c.g.s. units. The curves Q, B, T, refer respectively to 
magnetisation parallel to the quaternary, the binary, and the 
ternary axes; i.e. to the directions respectively of the edges, the 
face diagonals, and the body diagonals of a cubic crystal. At the 
higher fields, the order is T>B>Q; while in weak fields the 
order is reversed, the three curves crossing in the neighbourhood 
of H = 30. 
Weiss observes that this peculiarity does not present itself in 
all specimens. The curves given were obtained with a dodecahe- 
dral specimen from Brozzo, in Piemont. In the case of an 
octahedral specimen from Zillerthal, in the Tyrol, the curves are 
“in the same order, in high fields, and do not intersect in the 
neighbourhood of the origin.” This point is of importance in 
view of the results obtained in the present investigation. 
Fig. 2 shows the effect of magnetisation, in its own plane, of a 
disc cut parallel to the faces of the cube. The longitudinal effect, 
i.e. the magnetisation parallel to the external field, is shown in 
the large full curve. The eight-lobed curve (six lobes only shown) 
in the centre represents the component of magnetisation transverse 
to the external field. This component vanishes along directions 
parallel to the edges and the face-diagonals of the cube. The 
flatness of each loop on the side next the lines parallel to the 
edges of the cube (horizontal and vertical in the diagram), and the 
