166 Baron N. Schilling- on the Constant Currents 



perature approaches the boiling-point, but returns on cooling. 

 Moreover this operation may be repeated without the substances 

 suffering decomposition. Cudbear, camwood, logwood, and tur- 

 meric are selected as illustrations of the properties cited. 



Cudbear yields a brilliant orange fluorescent light, and is 

 visible in diffused daylight without the agency of a condensing 

 lens, which is necessary to show it in an alcoholic solution. 



Camwood exhibits a powerful apple-green fluorescence, 

 although wholly destitute of this property in aqueous or alco- 

 holic media. The spectrum of the fluorescent light is continuous 

 from E downwards, interrupted by two narrow faint shadings 

 situated at 3| and 5 of Sorby's scale. 



With regard to logwood, unless the castor- oil solution be sa- 

 turated, sunlight and a lens are requisite to bring out its fluo- 

 rescent character. The colour very much resembles that of 

 camwood, but is distinguished by its spectrum, which is conti- 

 nuous from b, but interrupted by two shadings at 4| and 5 J. 



Turmeric is well known to fluoresce powerfully in alcohol a 

 yellow-green, and in benzole a blue-green. In castor-oil, how- 

 ever, the fluorescent light is at least three times as bright as 

 in other fluids, and may be described as a vivid emerald-green, 

 evident in the dullest daylight ; but if a flat bottle of the solution 

 be placed on black velvet behind rather deep cobalt-glass when 

 the sun is shining, the phenomenon is of a most brilliant descrip- 

 tion, and without exaggeration may be compared to that pro- 

 duced by the beautiful uranium-glass. The spectrum furnished 

 by the fluorescent light is characterized by transmission of red 

 and green rays, and blue to F, with a faintly perceptible shading 

 at the yellow end of the green. 



These facts therefore show that, in studying the phenomena 

 of fluorescence, advantage should be taken, whenever possible^ 

 of this valuable solvent property of castor-oih 



XXVIII. The Constant Currents in the Air and in the Sea : am 

 Attempt to refer them to a common Cause. By Baron N. Schil- 

 ling, Captain in the Imperial Russian Navy. 

 [Concluded from p. 109.] 

 A S we are speaking of wave-motion, it will not be out of 

 •J—V. place to mention here a circumstance which will subse- 

 quently be of importance for our argument. 



It is that the theory of waves, which is commonly laid as a 

 foundation for all tidal phenomena, has called forth two views 

 which cannot possibly be both together correct. In the first 

 place, it is generally assumed that the flood tide rises just as far 



