556 Mr. C. W. Raffety on some Investigations of 



focussed upon the slit of the spectrograph, and a visual 

 examination made with an eyepiece. The flow of gas was 

 varied and the precise region o£ the flame image selected, 

 until the hydrocarbon band appeared at its brightest. Only 

 the main head at about \4314 was at all distinct ; but the 

 visibility of the fainter doublets on the more refrangible side 

 was taken as an approximate guide to the best conditions. 



A reproduction of one of the spectrograms is given in 

 fig. 12, PL XIII. The main series of lines forming the 

 " tail " is well shown ; for not only are the lines com- 

 paratively bright, but they are also free from the masking 

 effect of the continuous spectrum, since the latter does not 

 extend with appreciable intensity quite so far. 



The faint new series can be discerned converging to a 

 point situated between the first two (least refrangible) 

 members of the main " tail " series. 



In the case of lines so faint showing against a veil of con- 

 tinuous light, measurements of wave-lengths are attended 

 with considerable difficulty and some little uncertainty. 

 The following approximate values were obtained. The first 

 two columns are from photographs obtained with the 

 grating instrument, on which the lines appear very faintly, 

 and the third is from a spectrogram with the prism. 



Spectrogram 1. 



Grating. 

 X. 



4106-7 

 4095-0 

 4084-2 

 4075*1 

 40659 

 4059-3 



4052-6 



4047-2 



4043 : 4"" 



4040-1 



i037 : 6~" 



4031-8 ;"" 



4025 : 2 



Spectrogram 2. Spectrogram 3. 



Grating - Prism 



(determined graphically), (determined graphically). 



X. 



4094-8 

 4084-6 

 4074-0 

 4065-0 

 4059-0 

 4053-0 



4044-0 

 4039-5 



x. 

 4108 



4095-3 



4084-8 



4074-0 



4066-0 



4060-7 



4053-0 



4047-8 



4043*2 



4040-0 



4037-0 



4031-3 



The horizontal dotted lines in column 1 indicate that there 

 occurred lines in these intervals too faint to be measured. 



