88 
Proceedings of the Royal Irish Academy. 
tetrad line, and the same remark applies to the eleventh element, 
silicon. 
In the remaining six elements lying between carbon and silicon, 
what (for want of a better word) I may call a " contest " takes place 
between the lineal branch and the cubic branch as to which of them 
shall have the element, but in no case are two elements formed with 
the same valency. 
1 . In the triad line, nitrogen is formed on the lineal branch, but 
there is distinctly intimated the possibility of another element on the 
cubic branch, with the atomic weight 13, where the cubic having passed 
through boron, again intersects the triad line. 
2. On the dyad line, oxygen is formed on the lineal branch, but 
the possibility is shown of another element on the cubic branch, with 
the atomic weight 16*4. 
3. On the monad line, fluorine is formed on the cubic branch, 
with a possibility of another element on the lineal branch, of atomic 
weight 18. 
4. Again, sodium is formed on the cubic branch, with a possibility 
of an element on the lineal branch, with atomic weight 22. 
5. Magnesium is formed on the lineal branch, with a possibility of 
another element on the cubic branch, with atomic weight 25. 
And, lastly, aluminium appears on the cubic branch, with a possi- 
bility of another element on the lineal branch, of atomic weight 26. 
These two periods of seven elements each form the first two 
octaves of the chemical harmony of the universe ; but what are we to 
do with hydrogen, which remains alone, outside the harmony ? 
Mendelejeff thought that his six missing brothers and sisters were 
to be sought between hydrogen and lithium ; but Dr. Reynolds easily 
proved that they must be sought for behind hydrogen, which is the 
last note of the primeval octave. Are they to be found between zero 
and unity, or looked for ''behind the looking-glass " in the unknown 
land of negative atomicities, where heat, light, and electricity reside ? 
However this may be, I think it useful to point out a remarkable 
relation between hydrogen and the fourteen elements which follow it 
in atomic weight. 
If we take the common centre of gravity of the fourteen elements 
(regarded as equal weights), and join this point with the point re- 
presenting hydrogen, the line so found is very nearly parallel to the 
asymptote of the cubic curve drawn in Plate vi. 
The difference in direction between the two lines is only 20' arc. 
Hydrogen, the first born, and king of the elements, sits alone, 
