Refracted and Diffracted Light. 355 



light. Now, if the different colours were equally refran- 

 gible, the three images would correspond in size, and every 

 part of the surface would be white ; but, in consequence of 

 tbe different refrangibility of the different colours, the 

 violet image is larger than the green, and the green larger 

 than the red ; the violet, therefore, extends beyond the 

 green, and exhibits a ring of this colour unmixed with any 

 other; concentric with it, there is a ring of the green 

 extending beyond the red, where the white light com- 

 mences; but this ring is superposed by the violet, which 

 converts it to blue: It is evident that these rings, or 

 fringes, are formed of the most refrangible rays which pass 

 nearest the edge of the lens, where the light is the most 

 highly refracted ; and, consequently, that the rays of these 

 colours which intersect the most highly refracted part of 

 the less refrangible colours, to form the white light, adjoin- 

 ing the fringes, must pass through the lens at a distance 

 from its edges proportioned to the breadth of the fringes. 

 The other parts of the white surface are formed upon the 

 same principle; but the difference of refraction, arising 

 from this cause, decreases as we approach the central ray, 

 where it ceases; the images at this point being in exact 

 correspondence with each other, and unrefracted. 

 (To be continued.) 



Article V. 



On some Hydrargyro-Cyanurets. By Mr. George Henry 

 -Jackson. 



To the Editor of the Records of General Science. 

 Sir, — I shall feel obliged by the insertion in your excellent 

 Journal of the following account of the Hydrargyro- 

 Cyanurets. 



The fact that the cyanurets are capable of uniting with 

 one another just as two oxidized bodies, and of forming 

 definite compounds, has been long known; but those 

 double cyanurets which have been hitherto examined are 

 but few, and, amongst these few, perhaps the compounds of 

 the two cyanurets of iron, with the electro-positive cya- 

 2 a 2 



