[ 82 ] 
XII. 
GEOMETRICAL ILLUSTRATIONS OE ISTEWLAKDS' ANB 
MENDELEJEEE'S PERIODIC LAW OE THE ATOMIC 
WEIGHTS OF THE CHEMICAL ELEMENTS. Ry REV. 
SAMUEL HAUGHTON, M.D. (Plates lY.-VIII.) 
[Abstract.] 
PART L— THE FIRST AND SECOND PERIODS OF SEVEN ELEMENTS 
FOLLOWING HYDROGEN; OR, TRE CARBON-SILICON 
DOUBLE PERIOD. 
[Read April 28, 1888.] 
I ASSUME on tlie part of my readers a general knowledge of JSTewlands' 
Latv of Octaves^ of Mendelejeff's Periodic Law, and of Reynolds' graphic 
representation of the results arrived at by their successors on this re- 
markable subject. 
I reproduce, in Plate iv., with Dr. Reynolds' permission, the most 
recent graphic representation of the Periodic Law. 
In this diagram the elements are plotted according to their atomic 
weights and valencies ; the vertical co-ordinates being atomic weights, 
and the horizontal co-ordinates being valencies, counted (for conve- 
nience of plotting) positive or negative, according as the element belongs 
to an odd or even period of seven. 
First Period, or Carhon Period. 
ELEMENT. 
ATOMIC WEIGHT. 
VALENCY. 
1. Lithium. 
7 
Monad. 
2. Beryllium. 
9 
Dyad. 
3. Boron. 
11 
Triad. 
4. Carbon. 
12 
Tetrad. 
5. Nitrogen. 
14 
Triad. 
6. Oxygen. 
16 
Dyad. 
7. Fluorine. 
19 
Monad. 
