when viewed with closed eyes, presented a splendid spectacle like a 

 cluster of coloured stars, or rather of round planetary discs, brilliant 

 in green, yellow, orange, red, crimson and purple ! 



Besides the experiments thus far described, in which the spectral 

 images were viewed, for the most part, with gently closed eyes kept 

 steadily in the direction in which the objects were gazed on, the 

 differences, which were often very remarkable, produced by alter- 

 ations in the quantity of light admitted into the chamber of the eye 

 whilst the image was viewed, were also investigated. Sometimes 

 the smallest change in the light thus transmitted was found to alter 

 greatly the character of the spectrum. In certain cases, the com- 

 pressing of the eyelids, or the mere passing of the hands betwixt the 

 eyes and the light, would serve to change a negative picture into a 

 positive, or the colours, as viewed in the usual way, into their com- 

 plementary tints. 



The paper concludes with a considerable series of deductions, ap- 

 plications and general results. 1. As to the elucidation yielded by 

 these ocular spectra, of the theory of vision. 2. Of the principles of 

 binocular and simple vision. 3. Of the action of the retina for the 

 obliterating of impressed images, and the recovery of a normal con- 

 dition. 4. Of the nature of certain disturbing and dazzling effects 

 of vision by strong light. 5. Of the phenomena of certain spectral 

 illusions. 6. As to the practical use of the process of examining the 

 ocular spectra, for the determination of quantities of light relatively 

 intercepted by different portions or thicknesses of glass or other trans- 

 parent media. 7. For assisting in the determination of the relative 

 degrees of illumination of lamps, candles, &c., and of quantities of 

 light reflected from opake objects. 8. For aiding in the selection 

 and harmonizing of colours in ornamental and decorative depart- 

 ments of art. 9. For the examination of the condition of the inte- 

 rior of the eyes in certain states of disease. The author having had 

 the opportunity of trying this process in case of amaurosis, found 

 that it afforded a perfect picture of defects in the surface of the re- 

 tina of the eyes separately, when there was no visible defect, and 

 when the patient had no other perception of a diseased eye, or patch 

 on the retinal surface, except the partial distortion or interruption 

 of vision. Founded on this, the author suggests a plan of scotome- 

 trical examination of retinal defects, by which not only the accurate 





