Miscellaneous, 225 



Tverlge of glass, filled with the liquid under examination ; so that 

 while one edge of the sheet of light passed through an indefinitely 

 thin stratum of liquid, the other edge passing through the thick 

 extremity of the wedge, traversed a stratum of about three-fourths 

 of an inch thick. The light thus transmitted was decomposed by 

 a prism held parallel to the width of the sheet of light. Thus a 

 broad spectrum was thrown up for examination. That portion of 

 the spectrum adjacent to the thin edge of the wedge, and formed 

 by light which had traversed it, differed of course but little from 

 the solar spectrum ; but it was not found as might perhaps be 

 supposed, that the brilliancy of the colour of the spectrum uni- 

 formly diminished towards the thick end of the wedge. On the 

 contrary, some hues were found (with most media) to diminish 

 much more rapidly, and be extinguished much sooner than others; 

 so that while the one side of the broad spectrum, that towards 

 the thin edge of the medium was terminated by a straight line, 

 the other side was bounded by a deeply indented sinuous outline, 

 certain bands of colour extending much further towards the thick 

 end ot the wedge than others. For example, when a solution of 

 sesquichloride of chromium was the medium, the violet, indigo, 

 and yellow rays were almost immediately extinguished, leaving a 

 broad projection of blue and green, and a narrower, but much 

 longer, arm of red. Thus is explained the fact that dilute solu- 

 tions of this salt appear green, and concentrated solutions purple. 

 In this manner relations of colour between combinations contain- 

 ing a common' element were discovered, which the unaided eye 

 could not have detected. More than this, unfailing means of de- 

 termining the presence of certain elementary substances were 

 pointed out ; thus didymium invariably announces its presence in 

 solution, even when in small quantity, by two very black lines, 

 one in the yellow and one in the green. 



Interesting as these results are, and important as they may 

 become, the somewhat similar investigations pursued still more 

 recently by Kirchoff and Bunsen, are of surpassing interest and 

 importance. 



The distinctive hues imparted to flame by certain substances 

 have long served to indicate their presence in blow-pipe an- 

 alyses. It has been further observed, that different substances 

 impart distinctive appearances to the electric flame, appearances 

 especially remarkable when analyzed by the prism. It has been 

 reserved, however, for the philosophers above named, to examine 



Can. Nat. 5 Vol. VI. No. 3, 



