302 Mr. G. A. Hemsaiech and the Comte de Gramont on 



2840. The line X 2484 is only very feebly reversed in the 

 direct arc and, like the other lines, not reversed in water 

 arc and spark. 



c. Glass spectrograph. 



Wave- 

 lengths 



Ordinary arc 



Water are 





between 



between 





Grrapbite anode 



Graphite anode 





in 

 LA. 



and 



and Tin cathode. 





Tin cathode. 



1st phase only. 





3801-0 



15 cs 



10 b iv 





3907-2 







000 n 



enh. 



43301 







00 n 



enh. 



4524-7 



10 cs 



10 s 





4585-6 







1 



enh. 



4618-2 



|dd 



3 



enh. 



5100-4 



Z 



000 



enh. 



5224-5 







000 



enh. 



5332-6 



lddn 



10 n 



enh. 



5562-5 



2ddn 



15 



enh. 



55890 



2ddn 



10 



enh. 



5631-7 



8cs 



2 





5799-2 



2 del 



15 



enh. 



6149-6 



6cs 



On 





6452-8 



5dd 



20 



enh. 



6760 







1 



enh. 



6844-3 



1 dd 



4 



enh. 



§ 10. Explanation of Plates. 



The reproductions are made from enlargements of the 

 original negatives. Plate III. gives portions of the ultra- 

 violet regions of the spectra of Pb and Sn. a was obtained 

 by photographing in juxtaposition on the same plate the 

 spectra of the ordinary arc, water arc, and capacity spark 

 between Pb electrodes. The spark lines X 2950 and X 3018, 

 which are absent from the ordinary arc, are brought out in 

 the water arc. Noteworthy is the strong reversal of X 2833 

 in the water arc ; this line is reversed only feebly in the 

 ordinary arc and not at all in the spark. Photograph b 

 shows the spectra of the , ordinary and water arcs of tin 

 (metal electrodes). The most remarkable feature is the 

 prominence in the water arc spectrum of the two spark lines 

 X 3283 and X 3352, which are absent from the spectrum of 

 the ordinary arc. 



On Plate IV. are reproduced portions of the visible region 



