Royal Society. 149 



the light. The manner of making the observation most conveniently 

 is pointed out. 



6. These experiments are varied so as to show the various disten- 

 sions of the disc of a flame subjected to flexion between two edges, 

 according as we regard the various portions of the flame's spectrum 

 when seen by the prism. The red part is broadest, and when the 

 near approach of the edges to each other divides the disc into two 

 with a dark interval between them, that interval is the broadest in 

 the least refrangible rays. 



7. The experiments are further varied by using coloured glass 

 instead of refracting with a prism. 



8. The same phenomena are found to exist in all the other cases 

 of flexion as where it is combined with reflexion by the action of 

 specula, or by the effect of striated surfaces. There is always the 

 same difference in the effects produced by the different kinds of 

 homogeneous light. 



9. The same pheenomena are not so easily observed in the internal 

 fringes, or those of the shadow ; but the dark gray line in the axis 

 of the shadow, having a line of deep black on each side, is found to 

 vary in breadth and position in the different parts of its length cor- 

 responding to the colours of the spectrum, when a needle or other 

 small body is placed in that spectrum. 



10. The angle of inflexion is shown to be obtained by taking the 

 distance at which the internal fringes begin to appear ; and the pro- 

 portion of this angle in the red to the same angle in the violet is 

 ascertained. The deflexion (as deduced from Sir I. Newton's ex- 

 periments) is much greater than inflexion appears to be. He had not 

 observed the internal fringes of Grimaldi,to whom, however, he refers. 



11. The author states that the property in question, the different 

 flexibility of light, coexists with the other property, whatever it may 

 be, which disposes the different rays in fringes of different breadths ; 

 but he considers that the two properties are wholly independent of 

 each other. 



12. He thinks there is reason to believe that the dark intervals 

 between the fringes made in white light are only the dark tint of the 

 adjoining fringes, of which the red of one runs into the violet of the 

 other. The greatest care in repeating Sir I. Newton's experiment, 

 with the same distances and sizes both of the body and the beam, 

 leaves little or no doubt of the fringes running into each other. In 

 homogeneous light it is otherwise ; and there appear in that case to 

 be the intervals, as might be expected from the different flexibility of 

 the different rays. 



13. The fringes made in homogeneous light have a considerable 

 admixture of colours from the scattered rays ; so have the small 

 spectra by refraction made when a second prism is placed behind a 

 small hole in the screen, through which hole the rays of the spectrum 

 made by the first prism are successively passed. 



14. The phenomena of flexion by bodies placed in the portion of 

 the spectrum near the prism, and therefore white, are stated to be 

 not easily accounted for in any received theory. 



15. The Newtonian hypothesis of the different breadths of the 



