The funnel (shown flat as an isosceles triangle, standing on its apex) is a somewhat complicated structure, of the same type as that in sodium (Plate VI, 2), the difference consisting in the addition of one more globe, containing nine additional atoms.  The central globe is the same as in sodium, but the connecting rod differs.  We have here a regular arrangement of five globes, containing three, four, five, four, three atoms respectively, whereas sodium has only three bodies, containing four, six, four.  But copper and silver, its congeners, have their connecting rods of exactly the same pattern as the chlorine rod, and the chlorine rod reappears in both bromine and iodine.  These close similarities point to some real relation between these groups of elements, which are placed, in the lemniscates, equi-distant from the central line, though one is on the swing which is going towards that line and the other is on the swing away from it.

CHLORINE:  Upper part {12 funnels of 25 atoms 300
                     {Central globe 10
          Lower part same 310
          Connecting rod 19
                                             ——­
                           Total 639
                                             ——­
          Atomic weight 35.473
          Number weight 639/18 35.50
(The Atomic Weights are mostly from Erdmann, and the Number Weights are
those ascertained by us by counting the atoms as described on p. 349,
January, and dividing by 18.  Prof.  T.W.  Richards, in Nature, July 18,
1907, gives 35.473.)

BROMINE (Plate V, 3).—­In bromine, each funnel has three additional bodies, ovoid in shape, an addition of 33 atoms being thus made without any disturbance of form; two pairs of atoms are added to the central globe, and a rearrangement of the atoms is effected by drawing together and lessening the swing of the pair of triplets, thus making symmetrical room for the newcomers.  The connecting rod remains unchanged.  The total number of atoms is thus raised from the 639 of chlorine to 1439.  Over and over again, in these investigations, were we reminded of Tyndall’s fascinating description of crystal building, and his fancy of the tiny, ingenious builders busied therein.  Truly are there such builders, and the ingenuity and effectiveness of their devices are delightful to see.[20]

BROMINE:  Upper part {12 funnels of 58 atoms 696
                     {Central globe 14
          Lower part same 710
          Connecting rod 19
                                              ——­
                           Total 1439
                                              ——­
          Atomic weight 79.953
          Number weight 1459/18 79.944