1901 - 2 .] Mr J. Fraser on Constitution of Matter and Ether. 59' 
Now, I think the explanation of this variation of quantivalence 
will be found in the fact that some atoms are more compressible 
than others. I think it will be found that the atoms of invariable 
valency are closer-grained, and therefore nearer the limit of 
squeezability ; while those of variable quantivalence are more open- 
grained, and therefore more susceptible to compression. A differ- 
ence in the conditions of temperature or pressure, or both 
combined, might cause a greater or less number of monads or 
dyads, etc., to cling to the nucleus of the open-grained kind; while 
it is quite conceivable that, owing to the rigidity of the close- 
grained kind, and the comparative slow motion of their particles, 
a difference in the conditions of combination would have far less 
effect in causing variable quantivalence. Size of atom might 
also limit the variability, as it seems evident that only a few large 
atoms could be in touch with a small one. 
But why should the variable atoms change their valency two 
steps at a time ? it will he asked. To answer this, I must again 
point to the fact that in a compound molecule the component atoms 
group themselves symmetrically round the nucleus because, as it 
seems to me, they find a better hold as far away as possible from 
where their companions are attached to it, simply because the 
nucleus is less compressed at those points. Well, then, in order to 
illustrate my conception of this change in valency, suppose the atom 
which acts as a nucleus to be a perfect sphere, furnished with an 
equator and poles, and suppose a great circle to pass through each 
pole, cutting the equator at right angles. Let us now take as an 
example the atom of manganese mentioned above as our nucleus, 
and which can change its valency from a dyad to a hexad. First, 
then, we can have MnF 2 ; in which case we will suppose the two 
fluorine atoms to he attached one to each pole of the manganese 
nucleus. The molecule in this way will be perfectly symmetrical. 
The next change will be MnF 4 , that is, a fluorine atom attached 
to each pole, and one each attached to opposite sides of the equator 
where the great circle cuts it. The molecule in this way will be 
also perfectly symmetrical. We could not possibly make this a 
triad molecule with a fluorine atom attached to each pole unless 
we remove the two latter to some other parts of the sphere, and as, 
I presume, the condition which determined the change was either a 
decrease of temperature, or increase of pressure, or both, the twa 
