686 Scientific Proceedings, Royal Dublin Society. 
substances effects the spontaneous transformation of certain ethylene 
compounds into their isomerides. Thus the presence of traces of 
iodine causes the quantitative transformation of ethylic maleate into 
ethylic fumarate.* 
APPENDIX. 
The main ideas which form the basis of the foregoing inquiry 
viz. closest-packing, mutual repulsion of particles, ties or restraints 
on this mutual repulsion, are all old conceptions—they have been 
used by earlier writers and are still adopted by living scientists.” 
Nevertheless it seems desirable to put them collectively, as employed 
in the present case, into the shape of definite concepts clothed in 
precise language. 
The following is an attempt to do this, but the writer wishes it 
to be understood that the list of postulates here given is intended 
as 2 minimum one—that it is not to be regarded as complete for any 
purpose except the production of the effects under consideration, and that 
it is put forward merely as a proposal, for the purpose of eliciting 
the criticisms and suggestions of those who, in explaining or eluci- 
dating phenomena, have adopted the same or similar concepts. 
Proposed Concepts. 
1. Particles or centres of influence which are mutually repel- 
lent. - 
2. Kach particle to be destitute of polarity so that its 
influence on surrounding particles is not affected by turning it 
about its centre. 
3. Different kinds of particles to experience different degrees 
of repulsion from the same particle at the same distance. 
4. The mutual repulsion which any two of the particles exer- 
cise to diminish as the distance between them increases, and to be 
always some inverse function of this distance such that when the 
1 Hantzsch, loc. cit., p. 83. 
2 Comp. ‘‘ Molecular Constitntion of Matter,’’ by Sir William Thomson, in ‘‘ Pro- 
ceedings of the Royal Society of Edinburgh,”’ vol. xvi. p. 693; as to closest-packing, 
see p. 712; as to mutual repulsion of particles of more than one kind, see pp- 
699-700 ; as to constraints, see p. 699. 
