44 BLACK CIRCLE FIELD'S LENTICULAR PRISM. 



part of the molecule where the oxygen red ray is posited, 

 while the hydrogen Hue ray occupies 1.31 part of the whole 

 sphere, and in its then condensed state is in a lateral position, 

 and during the force of pressure, arising from emanation, is (for 

 the time) dispossessed of all polar influence, whence LIGHT is 

 LUMINOUS. But, remove that pressure of emanation, and im- 

 mediately the hydrogen blue ray expands to its full possession 

 of 8 parts in volume of the entire sphere, as described by No. 5, 

 Plate IV. When the nitrogen yellow ray in its turn occupies 

 the lateral position^ and the positive pole of the hydrogen blue 

 (always connected with the production of shade} is the only 

 point of polarity to which the negative pole of the oxygen red 

 ray can possibly be (by attraction) attached, and must conse- 

 quently, from the derangement of the organised polarity, pro- 

 duce shade and darkness in place of illumination. 



Hitherto we have confined our attention to the oblong spec- 

 trum produced by the Newtonian triangular prism, No. 1, 

 Plate L, we must now observe what becomes of the interfer- 

 ence of the black lines, by viewing the annular spectrum pro- 

 duced by Field's lenticular prism : this annular spectrum is 

 exhibited No. 2, Plate I. 



On viewing a black spot on a white ground, there appears 

 an interior circle of blue, and next in rotation between that 

 and the red, a distinctly defined dark circle, about J in breadth 

 of the preceding blue : next follows the red, and externally the 

 yellow, as before observed, occupying with well defined lines of 

 demarkation their respective areas, 



Now, it would appear that in this annular exhibition of the 

 three primary rays, the dark lines instead of being scattered 

 and diffused, as they are over the extended oblong spectrum, 

 now occupy in the annular spectrum a defined and continuous 

 space ; and where the refraction is produced from a dark central 

 spot on a white ground, this circle of shade is evidently visible ; 

 while on the contrary, on reference to No. 3, Plate I., where 

 the refraction emanates from a white central spot on a dark 



