32 Mr. T. Bayley on the Atomic Weight and the 



is represented by a symbol expressing its position as regards 

 other elements and its relations to them, whether axial as 

 among the members of a family, or lateral as between adjacent 

 elements in a series or cycle. Up to the present we have 

 recognized the following circumstances to be connected with 

 the properties of an element: — 



(a) Position of sequence in the series, 



(b) Proportionate position in the series, 



(c) Position in the cycle ; 



and we have seen that elements having the closest family 

 resemblances are most alike in respect of the first and last of 

 these, and most probably in all. 



Accompanying the periodic variations in the chemical pro- 

 perties of the elements by means of which they have been so far 

 systematically classified, are variations in their plrysical proper- 

 ties synonymous with the chemical variations, and so closely 

 coordinated therewith as almost irresistibly to urge the con- 

 viction that the two sets of phenomena (the physical and the 

 chemical) are intrinsically due to the same ulterior causes, or 

 stand in the sequence of cause and effect. 



The diagram, PL II. fig. 2, which is in some respects the 

 same as those published by L. Meyer in Die moderne Theorien 

 der Chemie, has been constructed for me by my friend Mr. 

 TTorrall : along the horizontal line as ordinate the elements 

 are set out, according to scale, in the order of atomic weights; 

 and the various curves are formed by joining points in the 

 abscissa? corresponding to each element. The main curve on 

 the diagram thus corresponds to the atomic volumes of the 

 elements, obtained by dividing the atomic weight by the den- 

 sity when known. In cases where the density is not known 

 the element has been simply passed by, a straight line being 

 drawn from the preceding to the succeeding element, or from 

 the nearest preceding to the nearest succeeding element of 

 known atomic volume. The effect of this is somewhat to 

 obscure the resemblance in form between the portions of the 

 curve corresponding to the cycles ; but it has the advantage 

 of making the diagram entirely a record of known facts. The 

 line of atomic volume is well worthy of attentive study, which 

 will reveal better than any array of words the singular resem- 

 blances and points almost of identity in atomic volume between 

 elements resembling each other quite as closely in chemical 

 properties. It will be seen how the alkali metals in every 

 case have the highest atomic volume, and how the metals with 

 the lowest atomic volumes (those occupying the troughs of the 

 curves) are metals with comparatively small affinities for 



