306 REPORT— 1880. 



(4) Photographic effects of electric spectra of different metals produced 

 hy transmitting the sparks through gases other than atmospheric air. 



The gases to be examined were passed tlirough a glass tube which 

 enclosed the electrodes ; on one side the part opposite the metal-points 

 was cut away and replaced by a thin piece of quartz. The genei'al results 

 of these experiments on the invisible rays are in harmony with those 

 already obtained for the visible rays by MM. Angstrom,' Alter, ^ and 

 Pliicker.^ They may be summed up as follows : — 



1. Each gas tinges the spark of a characteristic coloui' ; but no judg- 

 ment can be formed from this colour of the kind of spectrum which the 

 gas will famish. 



2. In most cases, in addition to the lines peculiar to the metal used as 

 electrodes, new and special lines characteristic of the gas, if elementary, 

 or of its constituents, if compound, are produced. When compound 

 gases are employed, the special lines produced are not due to the compound 

 as a whole, but to its constituents. 



Prof. Stokes's experiments on the fluorescent spectra of metals and 

 the diactinicity of solids and solutions corroborate the results obtained by 

 Dr. Miller. In his method of experimenting the substance to be observed 

 is introduced into the solvent, and the effect on the fluorescent screen 

 watched as solution gradually takes place ; in this way he was enabled to 

 seize the most charactei'istic phase of the absorption, and registered it on 

 paper by naeans of a pricking instrument devised by him for the pur- 

 pose. 



Some interesting results were also obtained by him regarding the 

 Absorption of the invisible rays by Alkaloids, Glucosides, ^'c. He found 

 that these bodies were intensely opaque for a portion of the invisible 

 rays, the mode of absorption being generally highly characteristic. The 

 solvents used were water, dilute sulphuric acid, dilute hydrochloric acid 

 and ammonia: all of these being sufficiently transparent to the rays under 

 examination, to answer the purpose. The effect of acids and alkalies on 

 the glucosides presented one uniform feature : when a previously neutral 

 sokxtion was rendered alkaline the absorption began somewhat earlier, 

 when rendered acid somewhat later. In the case of quinine and the other 

 bases observed, with one exception, the absorption, if altered at all, was 

 changed in an opposite manner to that in the case of the glucosides when 

 the base is set free by ammonia. Bands of absorption also appeared 

 when neutral substances were examined, e.g., in the case of coumarine 

 and paranaphthaline. 



In addition to experimenting on several minerals as to their trans- 

 parency for the rays which give rise to fluorescence. Prof. Stokes exa- 

 mined them also for the property of fluorescence itself. His researches 

 in this direction were rewarded by some interesting results. He found 

 that adularia exhibits a pair of bluish dots — the images of the tips of the 

 electrodes — when the rays of highest refrangibility are focussed on it ; as 

 the same phenomenon was observed with colourless felspas from different 

 localities, it is doubtless a property of silicate of alumina and potash. 

 The other case of interest relates to a particular variety of fluor-spa 

 found at Alston Moor. The specimen, when exposed to the spark passing 



' Pofff/endorff's Annalen, 1855, Bd. xciv. s. 141. 

 2 SiUiman's Journal, 1855, vol. xix. p. 213. 

 * Poggendorff" s Annalen, 1859, Bd. cvii. s. 497. 



