in the Modern Spectroscope. 31 



elements in actual chemical combination ; while, whenever the 

 heat is raised high enough to dissociate those elements, then im- 

 mediately their several spectra appear as elements ; and they give 

 spectra of fine lines only, sharp, well defined, usually far apart, 

 and not affecting in any degree to occupy the place of the bands 

 of the compound. 



How, then, came so egregious an error to grow up in the 

 modern world, as to mistake so very unlikely a spectrum and of 

 the most easily volatilized compound, and at the very beginning, 

 instead of end, of its burning, for the most refractory of all the 

 elements ? 



The history of errors is always instructive ; and the folio wing- 

 seems to have been its course in this carbon case. 



The Rise of the Myth of Carbon-vapour. 

 The Royal Society (acting unhappily through its secret com- 

 mittees) first patronized the mistake, by publishing in their 

 Philosophical Transactions Mr. Atfield's paper of 1862, p. 221, 

 wherein he examined, rather cavalierly*, what Professor Swan 



* As one example : — " The yellow-green (citron) band, composed," 

 says Mr. Atfield (p. 222), "according to the drawing accompanying Swan's 

 paper, of four lines, I find to contain six ; the green band to have five 

 instead of two." 



From this statement any one might be led to conclude that there was a 

 definite number of lines of equal observing importance in each band, that 

 Professor Swan had committed a grave error in alluding to only four and 

 two when there were really six and five, and that the new lines might be 

 in spectrum -place either before, behind, or amongst Swan's lines in order 

 of dispersion — entirely therefore destroying the value of his observed spec- 

 trum-places of those lines reckoned as first, second, third, &c. of each 

 band, counting from the less-refrangible side. 



Yet, in place of this, the new lines only tack on to the fainter and more - 

 refrangible end of a vanishing series, of which Professor Swan correctly 

 described all the components, from the first and brightest up to the last 

 and faintest one certainly visible in his apparatus. Mr. Atfield, by an 

 unlimited use of oxygen in place of common air, was able, in a rich London 

 laboratory, to produce more brilliance in the light operated on by his spec- 

 troscope, and therefore could carry on the vanishing series, as might well 

 have been expected, a little further; and since then M. Morren, in Paris, 

 has carried it on further still. But all these additional lines are hardly 

 equal even in collective light and importance to the last line of the series 

 previous to them ; nor do they alter the place of the brighter preceding 

 lines in any degree, either as being the first, second, &c. of each band, or 

 in their recorded wave-lengths. 



It is also worthy of note, that there is neither a plate- view, nor a single 

 measured-scale place of any one spectrum-line throughout the whole of 

 Mr. Atfield's paper — an omission of all that is accurate in spectroscopy, of 

 all that has tended to make it a high science, which can only be explained 

 (in a memoir crowned by being printed'inthe Philosophical Transactions of 

 the Royal Society of London) by its one chief burden (viz. putting pure 

 carbon vapour for hydrocarbon) having been grateful to the then already 

 formed prejudices of the secret committee who passed it. 



