4(l4 Proceedings of the Royal Insiitution, 



is so beautiful and interesting, that he thought some benefit to science 

 nHl&t^plThgfrom the researches to which he thus directed the atten- 

 ti<)h*6C'bthers; for wherever the power lies in our organs of vision, 

 th^ curious effects of contrary spectra are interesting to investigate, 

 add important to knoWi'-^^' ^'*'i^ lia^ u:- j )uu.-6tlj^i, 



< Mr. Brockedon mentioned the rese^thes of Mr. Field of Isietrorth^ 

 irito this subject, and exhibited some instruments which Mr. Field had 

 l^t'to him, by which he measured the combinations and intensities 

 of icoiour. Three hollow wedges, glazed at the sides, and made to 

 contain coloured liquids, were placed in a frame, so that a ray of light 

 nughtbe made to pass through all or any of them at the same time : 

 the red wedge was filled with liquid madder ; the blue wedge, with 

 sulphate of copper ; and the yellow, with chromate of lime, or tincture 

 of saffron. These liquids were of such intensity of colour, that a ray, 

 passed through the centre of each, would fall on paper, which received 

 also a similar coloured ray from a prism : thus charged and placed in 

 the frame, they were adjusted until the ray of light passing through 

 all three was white : when this was the case, withdrawing the red 

 wedge left a pure green ; taking out the yellow, left purple ; on re- 

 moving the blue, orange ; and, taking the centre of each wedge for 

 zero, by graduating the top of the wedge, the proportionate quan- 

 tities for the production of white light were unequal, but agreed sin- 

 gularly with those stated by Sir Isaac Newton. These three wedges 

 were, from intensity and variety, capable of producing every possible 

 tint and colour. To this instrument Mr. Field had given the name 

 of chromometer. Another instrument invented by Mr. Field was 

 also shewn, which, having a piano-conical lens — or, as Mr. Field 

 called it, a lenticular prism, at one end, objects seen through it were 

 beautifully fringed with colour, and presenting an involution of forms 

 singularly curious. With this instrument he could so direct the dispersed 

 light, that a yellow ray falling upon one eye, and a blue ray upon 

 the other, these would, with both eyes open, excite the idea from both 

 ot green. Mr. Brockedon, in trying some experiments with the flat 

 square bottles which contained the coloured fluids for the wedges, 

 produced the same effect, laying on the eyes the flat sides of the 

 bottles, one containing yellow, and the other blue ; the impression 

 of both at the same time was green ; even with one eye, looking long 

 at either colour, its complementary spectra would neutralize it to a 



