582 Scientific Proceedings, Royal Dublin Society. 
the place of maximum temporary strain, and the latter will natu- 
rally be some plane which runs between nearest parts of different 
nature. 
It seems therefore not improbable that planes of cleavage of 
the assemblages in question will be planes on the opposite sides of 
which contiguous parts which face one another are most diverse. 
Polar properties. 
All polar properties of homogeneous assemblages, such for 
example as would correspond to pyro-electric, or piezo-electric 
phenomena, since they depend on dissymmetry in opposite direc- 
tions, will be impossible in all cases where centres of inversion are 
present, but may be looked for, to a greater or lesser extent, in all 
other cases. It does not appear that any peculiarity of form or 
arrangement of matter, other than that which is involved by the 
display of one or other of the possible types of homogeneity which 
are destitute of such centres, is necessary to account for any kind 
of mere opposite polarity. 
II.—Partial dissolution in a symmetrical manner of the ties which 
hold the parts of a linked homogeneous assemblage in their 
places, and subsequent partial destruction of the homo- 
geneity so that the assemblage breaks up into groups in 
each of which the parts are symmetrically placed with 
respect to one another, while the arrangement and orien- 
tation of the groups has become more or less irregular 
and fluctuating ; the groups thus resembling the theoretical 
molecules of stereochemistry.’ 
Of the groups formed by linking together two or more balls: 
1 Dr. Hantzsch defines Stereochemistry thus :—<‘‘ Stereochemistry demands the- 
single necessary supposition that the simplest group units, 7.e., the molecules, as well as 
all other complex groupings, have three dimensions. It requires, however, at least in 
its present stage of development, no definite concept as to the manner or origin of the: 
holding together of the atoms within the molecule, i.e., as to the nature of chemical 
affinity ; nor as to the kind and origin of the combining proportions of the different 
atoms, i.¢., as to the nature of valency. At present it requires only the premiss, signally 
established by the existence of isomerism, that the atoms, as found within the molecule, 
are not in a chaotic condition, but are, within certain limits, arranged in stable 
