308 Royal Society .— 



the vapour of ether, of chloroform, and of oil of turpentine was sub- 

 stituted for that of benzol, gave effects which, though perceptible, 

 were much less marked. An arbitrary scale is laid clown, by which 

 a comparative estimate of the absorptive power of each compound, 

 whether solid, liquid, or gaseous, may be effected with tolerable 

 accuracy. 



With a view of facilitating the production of a spectrum on a flat 

 field, at a uniform distance at all points from the prism, the author 

 instituted a series of experiments, in which a small metallic speculum 

 was substituted for the lens of rock-crystal ; but the loss of chemical 

 power in the reflected rays was so considerable, and this loss occurred 

 so unequally at different points, that the method was abandoned. 

 The results of the photographic action of light reflected at an angle 

 of 45° from the polished surface of several of the principal metals is 

 given. The reflexion from gold, although not very intense, was 

 found to be more uniform in quality than that from any other metal 

 that was tried. Burnished lead also gave very good results- The 

 reflexion from silver is singularly deficient in some portions of the 

 less refrangible rays, although in most other parts the reflexion is 

 tolerably perfect, except for rays of extremely high refrangibility. 



2. The Electric Spectra of the Metals. — The author proceeds 

 then to detail his experiments upon the spectra obtained by causing 

 the sparks produced by the secondary current from the induction-coil 

 to pass between electrodes composed of various elementary sub- 

 stances, and he gives photographs of the impressions obtained from 

 collodion negatives of a considerable number of different elementary 

 bodies. The spectra were procured by arranging a quartz -train in 

 the manner already described. Among the elements so examined 

 are the following : — 



Platinum. 



Arsenic. 



Copper. 



Palladium. 



Tellurium. 



Aluminum. 



Gold. 



Tungsten. 



Cadmium. 



Silver. 



Molybdenum. 



Zinc. 



Mercury. 



Chromium. 



Magnesium. 



Lead. 



Manganese. 



Sodium. 



Tin. 



Iron. 



Potassium. 



Bismuth. 



Cobalt. 



f Graphite, and 

 \ Gas-coke. 



Antimony. 



Nickel. 



The commencement of each spectrum in its less refrangible portion 

 is similar in nearly all cases ; and as it is this portion only which is trans- 

 missible through bisulphide of carbon, this circumstance explains the 

 similarity of all the spectra procured by the author from different 

 metals in his earlier experiments, already laid before the British Asso- 

 ciation. In the more refrangible parts of the spectrum great and cha- 

 racteristic differences between the results obtained with the different 

 metals are at once manifest. In some cases, as in those of copper and 

 nickel, the action is greatly prolonged in the more refrangible extre- 

 mity, whilst the intense and highly characteristic spectrum of magne- 

 sium is much shorter. 



