26 Mr. P. Smyth on Carbon and Hydrocarbon 



twilight and phosphorescence in many seas, and then sent a 

 second paper to the Royal Astronomical Society. And that one 

 they did print in the same year, with a very good engraving, 

 too, of my several pairs of spectra just as they were simultane- 

 ously seen in my spectroscope — one member of each such pair 

 being, for reference sake, invariably the bands and lines of the 

 carbon- or hydrocarbon-spectrum, precisely as Dr. Watts is now 

 proposing it in 1874, and as, too, I have since found that it 

 was used before my time in telespectroscopy by the eminent 

 Lewis M. Rutherford, of New York, and differing only in the 

 manner of producing the spectrum from what Dr. Huggins 

 actually accomplished on the comet of 1866 and on several others 

 since then. 



Truly, therefore, I have nothing to say against the principle of 

 the method proposed now by Dr. Watts as his own ; but I am 

 sorry to differ from him in the instrumental description which 

 he gives of the visible spectrum concerned, and which will affect 

 the observations of all persons who use it as a standard of 

 reference. 



Mensuration of the Spectrum referred to. 



The Doctor remarks, sagely enough, that for cometary work 

 the reference-spectrum should be of "feeble intensity;" why 

 then does he not examine it in that shape, viz. as given by the 

 blue base of the flame of a small alcohol lamp, or the all but 

 vanishing globule of flame when a common gas-light is on the 

 point of going out from inanition ? 



But in place of so doing, he takes brilliant olefiant gas and 

 burns it with oxygen " at the platinum nozzle of an oxyhydrogen 

 blowpipe." 



That in itself is quite enough to introduce some variations in 

 the spectrum of a volatile chemical compound; and he gets still 

 more when he examines it, not under the small dispersion usu- 

 ally employed on comets, but with the tremendous dispersion of 

 six dense flint prisms. For to such an overpowerful instrument 

 the appearance of the several " bands " (which is the character- 

 istic feature under small dispersion) is almost annihilated, being 

 replaced by more or fewer of the successive and almost isolated 

 lines of which those bands are ultimately composed in nature, 

 but which fine lines no one has ever seen, or need expect to see, 

 in the spectrum of any ordinary comet. 



The first step, therefore, in the Doctor's instructions to astro- 

 nomers might well have been on the " bands," and should have 

 been very complete with them ; what will not, therefore, be any 

 one's surprise to find that though the spectrum in question 

 consists notably and notoriously (even when prepared from 



