148 MR. CHARLES DE WATTEVILLE ON FLAME SPECTRA. 



each spectrum, but, except in the case of the metals belonging to the iron group, 

 where a considerable number of feeble lines may have been omitted, they do not 

 cause much trouble. Their intensity is, on the whole, weak compared with that of 

 the lines being studied, and they only extend to a small portion of the total length of 

 the spectrum. In particular, the characteristic regularity in the disposition of the 

 carbon bands enables them to be very easily recognised. I have besides made an 

 exposure for 24 hours three times the normal exposure with the non-luminous 

 flame produced by the apparatus working as usual, but without the addition of any 

 salt, and the photograph thus obtained has been very useful for comparison. I have 

 also found valuable information in the descriptions of these accessory spectra given 

 by EDER and V A LENTA. 



As to the intensities of the lines, it is well known how uncertain their estimation 

 must be, depending as it does upon the judgment of the observer, upon the apparatus 

 used, and also upon the unequal sensitiveness of the photographic plate to the 

 different rays. The numbers to be given afterwards do not claim any more than to 

 indicate approximately the relations between the intensities of the lines in a certain 

 region. For this purpose I have combined the results obtained from the three 

 spectra photographed for each metal, for a very strong ultra-violet line, which would 

 have an intensity represented by 10 in the spectrum given by the quartz prism, might 

 only have an intensity represented by 2 in the spectrum given by the grating. This 

 correction has been impossible in the green portion of the spectrum on account of the 

 plate, and it is certain that in this region the errors in the estimation of the intensity 

 are greatest. 



In the following tables, in order to facilitate comparison, I have tabulated the 

 measurements of the arc spectra made by KAYSER and RUNGE. Only those lines 

 have been included whose wave-lengths lie between the limiting wave-lengths 

 observed in the flame spectrum of each metal. Moreover, all those lines in the arc 

 spectrum which are of less intensity than the weakest of those in the flame spectrum 

 are not mentioned at all. Thus, .for instance, when no line of intensity lower than 6 

 in the arc spectrum is found in the flame spectrum, 1 shall indicate for the arc 

 spectrum only those lines which have intensities 10, 9, 8, 7, and 6, but shall include 

 those of these intensities which are missing in the flame spectrum. 



With some metals the flame spectrum contains bands of a more or less complicated 

 nature in addition to the lines. Such is the case, for instance, with magnesium, 

 barium, strontium, calcium, copper, tin, and manganese. The study of these bands 

 and the nature of the compound to which they are due, forms no part of the present 

 investigation. The accompanying tables therefore contain only the lines which are 

 ascribed to the metals. 



