468 Molecules, Ultimates, Atoms, and Waves. [October, 



fact that, in several instances where these originate waves 

 of several different definite lengths, one or more of those 

 definite waves are common to two or more diverse chemical 



o 



ultimates. Thus, M. Angstrom notes no less than eight 

 waves in different parts of the spectrum as being common 

 to iron and titanium, three common to iron and calcium, 

 three to iron and nickel, 1 to iron and sodium, one to iron 

 and magnesium, one to iron and manganese, one to iron and 

 barium, one to cobalt and titanium, one to titanium and 

 calcium, and one to calcium and manganese. Several 

 other instances of similar coincidences are noticed in a paper 

 by the Rev. T. R. Robinson, "On Spectra of Electric 

 Lights" (Phil. Trans., 1862, p. 939). In particular he 

 notes that the line c, which is one of those produced 

 by hydrogen, is also common to six metals, whatever be 

 the nature of the gas through which the spark between 

 the electrodes passes. He specifies another line in the 

 yellow region, which is, under similar circumstances, com- 

 mon to five metals, and a third in the blue also common to 

 five metals. Mr. Huggins in his tables likewise notes a 

 line near D as being common to arsenic and zinc, the longer 

 D itself as being common to sodium and lead, the shorter d 

 to sodium and barium. He has also found a line nearly 

 midway between d and E common to tellurium and nitrogen, 

 one a little beyond e common to oxygen and arsenic, and 

 one a little beyond f common to nitrogen and chromium. 



Of these phenomena, as well as of the multiplicity of 

 lines shown by some of the metals, the supposition that 

 the chemical elements are compounded of more minute 

 atoms supplies a simple explanation. As the lines are 

 supposed to be produced by the vibrations, not of the 

 ultimates themselves, but of their constituent atoms, and to 

 depend on the intrinsic inertia of these latter, when the 

 same line is found to be common to two or more diverse 

 metals or other elements, the most obvious inference is that 

 the ultimates of those metals or other elements contain the 

 same sort of atoms in combination with others of diverse 

 kinds. Thus the same species of atom which, in the 

 ultimate of hydrogen, produces the line c, occurs also in 

 the ultimates of six metals, associated with a variety of 

 other atoms having different periods of vibration. The cir- 

 cumstance also noted by the observers above named, that 

 the same line will appear with diverse degrees of relative 

 brightness in the spectra of the different elements in which 

 it occurs, is also easily explained by supposing that the 

 atom, whose vibrations originate that line, occurs in greater 



