§ =78.= A remarkable property of the atomic weights was discovered, in the sixties, independently by Lothar Meyer and Mendeléeff. They found that the elements could be arranged in rows in the order of their atomic weights so that similar elements would be found in the same columns. A modernised form of the Periodic Table will be found on pp. 106, 107. It will be noticed, for example, that the “alkali” metals, Lithium, Sodium, Rubidium and Cæsium, which resemble one another very closely, fall in Column 1; the “alkaline earth” metals occur together in Column 2; though in each case these are accompanied by certain elements with somewhat different properties. Much the same holds good in the case of the other columns of this Table; there is manifested a remarkable regularity, with certain still more remarkable divergences (see notes appended to Table on pp. 106, 107). This regularity exhibited by the “elements” is of considerable importance, since it shows that, in general, the properties of the “elements” are _periodic_ functions of their atomic weights; and, together with certain other remarkable properties of the “elements,” distinguishes them sharply from the “compounds.” It may be concluded with tolerable certainty, therefore, that if the “elements” are in reality of a compound nature, they are all, in general, compounds of a like nature distinct from that of other compounds. THE PERIODIC TABLE OF THE CHEMICAL ELEMENTS. +-------+-------+-------+-------+-------+-------+-------+-------+--------+ | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +-------+-------+-------+-------+-------+-------+-------+-------+--------+ | |[Hydro-| | | | | |Hydro- | | | |gen][a]| | | | | |gen | | | |[H = | | | | | |H = | | | |1·008] | | | | | |1·008 | | +-------+-------+-------+-------+-------+-------+-------+-------+--------+ |Helium |Lithium|Gluci- |Boron |Carbon |Nitro- |Oxygen |Fluo- | | | | |num | | |gen | |rine | | |He = |Li = |Gl = |B = |C = |N = |O = |F = | | |4·00 |6·94 |9·1 |10·9 |12·005 |14·008 |16·00 |19·0 | | +-------+-------+-------+-------+-------+-------+-------+-------+--------+ |Neon |Sodium |Magne- |Alumin-|Silicon|Phos- |Sulphur|Chlo- | | | | |sium |ium | |phorus | |rine | | |Ne = |Na = |Mg = |Al = |Si = |P = |S = |Cl = | | |20·2 |23·00 |24·32 |27·1 |28·3 |31·04 |32·06 |35·46 | | +-------+-------+-------+-------+-------+-------+-------+-------+--------+ |Argon |Potas- |Calcium|Scan- |Tita- |Vana- |Chro- |Manga- |Iron | | |sium[b]| |dium |nium |dium |mium |nese |Fe = |