[Illustration:  PLATE XIII.]

ALUMINIUM (Plate XIII, 1), the head of the group, is, as usual, simple.  There are six similar funnels, each containing eight ovoids, below which is a globe.

ALUMINIUM:  6 funnels of 81 atoms 486
Atomic weight 26.91
Number weight 486/18 27.00
GALLIUM (Plate XIII, 2) has two segments in every funnel; in the segment to the left a “cigar” balances a globe, equally six-atomed, in that of the right, and the globes to right and left are four-atomed as against three-atomed.  In the next row, the smaller contained globes have six atoms as against four, and the cones have respectively seven and five.  By these little additions the left-hand funnel boasts one hundred and twelve atoms as against ninety-eight.

GALLIUM:  Left segment 112 atoms }
         Right segment 98 " } = 210
         6 funnels of 210 atoms 1260
                                        ——­
         Atomic weight 69.50
         Number weight 1260/18 70.00
INDIUM (Plate XIII, 3) repeats the segments of gallium exactly, save in the
substitution of a sixteen-atomed body for the seven-atomed cone of the
left-hand segment, and a fourteen-atomed body for the five-atomed
corresponding one in gallium.  But each funnel now has three segments
instead of two; three funnels out of the six contain two segments of type A
and one of type B; the remaining three contain two of type B, and one of
type A.

INDIUM:  Segment A 121 atoms
        Segment B 107 "
        3 funnels of 2 A and 1 B ([242 + 107] 3) 1047
        3 " " 2 B and 1 A ([214 + 121] 3) 1005
                                                    ——­
                                         Total 2052
                                                    ——­
        Atomic weight 114.05
        Number weight 2052/18 114.00
The corresponding negative group, phosphorus, arsenic, and antimony, run on
very similar lines to those we have just examined.

[Illustration:  PLATE XIV.]

PHOSPHORUS (Plate XIV, 1) offers us a very curious arrangement of atoms, which will give some new forms in breaking up.  Two segments are in each funnel, in fact the only two of group III a which do not show this arrangement, or a modification thereof, are aluminium and arsenic.

PHOSPHORUS:  Left segment 50 atoms
            Right segment 43 "
                          —­
                          93
            6 funnels of 93 atoms 558
            Atomic weight 30.77
            Number weight 558/18 31.00
ARSENIC (Plate XIV, 2) resembles aluminium in having eight internal
sub-divisions in a funnel, and the ovoids which form the top ring are
identical, save for a minute difference that in aluminium