230 



Profs. Liveing and Dewar. 



[May 19, 



4289*44 and 4274*63 are both close doubles, with the chromium lines 

 the less refrangible. The latter line is difficult to resolve. 



5856*6 is plainly resolvable, the calcium line more refrangible than 

 the nickel line. 



5480*29. This is a double line of titanium, and the strontium line 

 is more refrangible than either titanium line. They form a not very 

 close triplet. 



5424*8. The barium line lies between the titanium line and the iron 

 line next it (5423 7), and the iron line is a very little more refrangible 

 than the barium line. 



The indium line 4101*2 we found very difficult to separate from the 

 hydrogen line (h), as the latter had to be taken from the spark in a 

 tube, and is both faint and diffuse, but several observations all led 

 to the conclusion that the indium line is very slightly less refrangible 

 than that of hydrogen. 



We have also directly compared the iron line at 5316*07 with the 

 solar spectrum, and found that the iron line corresponds with the less 

 refrangible of the two solar lines at this place, so that the coronal 

 line is in all probability the other line of the pair. 



There are still a few cases of supposed coincidences which we have 

 not examined. The results which we have recorded strongly 

 confirm Young's observations, and leave, we think, little doubt 

 that the few as yet unresolved coincidences either will yield to a 

 higher dispersion, or are merely accidental. It would indeed be 

 strange, if amongst all the variety of chemical elements, and the still 

 greater variety of vibrations which some of them are capable of 

 taking up, there were no two which could take up vibrations of the 

 same period. We certainly should have supposed that substances like 

 iron and titanium, with such a large number of lines, must each con- 

 sist of more than one kind of molecule, and that not single lines, but 

 several lines of each, would be found repeated in the spectra of some 

 other chemical elements. The fact that hardly single coincidences 

 can be established is a strong argument that the materials of iron and 

 titanium, even if they be not homogeneous, are still different from 

 those of other chemical elements. The supposition that the different 

 elements may be resolved into simpler constituents, or into a single 

 one, has long been a favourite speculation with chemists ; but how- 

 ever probable this hypothesis may appear, a priori, it must be 

 acknowledged that the facts derived from the most powerful method 

 of analytical investigation yet devised give it scant support. 



Appendix. May 13, 1881. 



The following supposed coincidences have been resolved, in addition 

 to those before mentioned : — 



