186 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



weight 12.25 instead of 12.00. Of recent years a great advance in 

 the accuracy of the determinations of atomic weights has been made, 

 chiefly owing to the work of Richards and his pupils, of Gray, and of 

 Guye and his collaborators, and every year an international committee 

 publishes a table in which the most probable numbers are given on 

 the basis of the atomic weight of oxygen being taken as 16. In 

 the table for 1911, of 81 elements no fewer than 43 have recorded 

 atomic weights within one-tenth of a unit above or below an integral 

 number. My mathematical colleague, Karl Pearson, assures me 

 that the probability against such a condition being fortuitous is 

 20,000 millions to one. 



The relation between the elements has, however, been approached 

 from another point of view. After prehminary suggestions by 

 Dobereiner, Dumas, and others, John Newlands in 1862 and the 

 following years arranged the elements in the numerical order of 

 their atomic weights and published in the Chemical News of 1863 

 what he termed his law of octaves — that every eighth element, like the 

 octave of a musical note, is in some measure a repetition of its fore- 

 runner. Thus, just as C on the third space is the octave of C below 

 the line, so potassium, in 1863 the eighth known element numerically 

 above sodium, repeats the characters of sodium, not only in its 

 plrysical properties — color, softness, ductility, malleability, etc. — 

 but also in the properties of its compounds, winch indeed resemble 

 each other very closely. The same fundamental notion was repro- 

 duced at a later date and independently by Lothar Meyer and Dmitri 

 Mendeleeff; and to accentuate the recurrence of such similar ele- 

 ments in periods, the expression "the periodic system of arranging 

 the elements" was applied to Newlands's arrangement in octaves. 

 As everyone knows, by help of this arrangement Mendeleeff predicted 

 the existence of then unknown elements under the names of eka- 

 boron, eka-aluminium, and eka-silicon, since named scandium, 

 gallium, and germanium by their discoverers, Cleve, Lecoq de Bois- 

 baudran, and Winckler. 



It might have been supposed that our knowledge of the elements 

 was practically complete; that perhaps a few more might be dis- 

 covered to fill the outstanding gaps in the periodic table. True, a 

 puzzle existed and still exists in the classification of the rare earths, 

 oxides of metals occurring in certain minerals; these metals have 

 atomic weights between 139 and 180, and their properties preclude 

 their arrangement in the columns of the periodic table. Besides 

 these, the discovery of the inert gases of the atmosphere, of the 

 existence of which Johnstone Stoney's spiral curve, published in 

 1888, pointed a forecast, joined the elements like sodium and potas- 

 sium, strongly electro-negative, to those like fluorine and chlorine, 

 highly electro-positive, by a series of bodies electrically as well as 



