144 EEPOKT— 1882. 



lines, or in certain cases even shorb lines, appear as long lines in the 

 spectra taken from solutions. 



The graphic characteristics of the lines seen in various metallic 

 spectra may thus be classified as — 



1. Continuous lines. They extend the whole length of the spark, 

 and are accurate representations of the spectroscope slit. 



2. Discontiyiuous lines. Those whose length is not so great as the 

 distance between the electrodes. 



3. Extended lines. Sharp lines which extend above and below the 

 edge of the spectrum, or, in other words, above and below the points of 

 the electrodes. 



4. Blotted lines, or lines surrounded by a nimbus. 



5. Nebulous lines, or those which are destitute of the sharp clear-cut 

 appearance of most metallic lines.' 



(4) Insoluble compounds give no spectra when mixed with water or 

 glycerine and exposed to the spark. The non-metallic constituents of 

 salts do not yield any marked series of lines, and therefore do not obscui'e 

 the metallic spectra. 



(5) Experiments have been made to determine the extent of dilution 

 which serves to modify in various ways the spectra of solutions of 

 metallic salts, and that which finally causes the extinction of the most 

 persistent line or lines. The sensitiveness of the reaction varies with 

 different elements and with the period of exposure, the intensity of the 

 spark, and other conditions ; I have no difficulty whatever, when work- 

 ing in the manner here indicated, in recognising spectra yielded by solu- 

 tions which contain no more than xTnyot'i of a^jer cent, of calcium, silver, 

 copper, and ToTrT7TT^^ ^^ b. per cent, of manganese. 



Report of the Committee, consisting of Professor RoscoE, Mr. 

 LoCKYER, Professor Dewar, Professor Liveing, Professor Schuster, 

 Captain Abney, cwicZ Dr. W. Marshall Watts (Secretary), ap- 

 jjointed to prepare a neiv series of Tables of Wave Lengths of 

 the Spectra of the Elements. 



The Committee has but little to report at present. An instrument for 

 the more exact performance of the process of graphical interpolation has 

 been constructed for the Committee, by Messrs. Cooke & Sons, of Tork, 

 at a cost of 20L This instrument has, however, only been in the hands 

 of the Committee for a few weeks. 



The Committee hopes to be in a position to make a fuller report at 

 the next meeting of the Association, and it desires to be reappointed. No 

 further grant of money ia at present needed. 



See Scientific Transactions of the Royal Dublin Society, vol. i. ser. 2, p. 232. 



