( 170 ) •* [April, 



III. MOLECULES, ULTIMATES, ATOMS, AND 



WAVES. 

 By Mungo Ponton, F.R.S.E. 



Part I. 



/^.HEMISTS have, for a considerable number of years, 

 x ' recognised the convenience of distinguishing the par- 

 ticles of chemical compounds by the term "molecules," 

 reserving the term " atoms " for those of the chemical 

 elements ; but the time seems now to have arrived when it 

 has become needful to make a further discrimination. This 

 need has been rendered manifest by the results of spectrum 

 analysis. The word "atom" conveys the idea of a particle 

 incapable of being analysed ; but the spectrum has shown 

 the particles of the chemical elements to be otherwise con- 

 stituted. Had they been simple homogeneous masses of 

 definite size and weight, each element, when thrown into 

 vapour and rendered incandescent, would have exhibited in 

 the spectrum only a single bright line: because every par- 

 ticle of the element being precisely alike would, when in 

 the vapourous state, and freed from all extraneous influences, 

 have vibrated in exactly the same periods of time, and so 

 have originated luminous waves of only one definite length 

 and period. The discoveries of Messrs. Bunsen and 

 Kirchhoff, however, and of other labourers in the same field 

 of research, have shown that the chemical elements, when 

 in the state of glowing vapour or gas, exhibit more than one 

 bright spectral line — some of them, indeed, a large number 

 of distinct lines of various degrees of brightness, in widely 

 different regions of the spectrum. Even hydrogen, the 

 element which is at once the lowest in specific gravity, and 

 the lightest in the scale of chemical equivalents, exhibits 

 four bright spectral lines, while iron presents a large number. 

 The law of chemical combination by equivalent weights 

 appears to exclude the supposition that the ultimate particles 

 of any element differ in size and weight — the equivalent 

 being merely an average. For the smallest quantity of the 

 vapour of any chemical element shows the same number 

 and kind of lines as any greater quantity ; while there is an 

 extreme improbability that this should be the case, did the 

 ultimate particles differ in size and weight, and were the 

 combining proportion merely a general average of those 

 diverse weights. The only alternative conclusion appears 

 to be, that each ultimate particle of the element consists of 



