SLCT. XL. i. OCULAR SPECTRA. 



SEC T. XL. 



On the OCUIAR SPECTRA of Light and Colours, 

 by Dr. R. W. Darwin, of Shrevvfbury. Re- 

 printed by Permiflion, frtfrn the Philofophical 

 Tranfadions, Vol. LXXVI. p. 3*3. 



Speclra of four kinds. I . Activity of the retina in vi- 

 fwn. 2. Speflrafrom def eft of fenfibility. 3. Spec- 

 tra from exccfs of fenfibility. 4. Of dire ft ocular 

 Spedra. 5. Greater Jlimulus excites the retina into 

 fpafmodic aclion. 6. Of reverfe ocular fpeclra. 7. 

 Greater flimulus excites the retina into various fuc- 

 cejjiye fpafmodic aclions. 8. Into fixed fpafmodic 

 atJion. 9. Into temporary paralyjis. 10. Mifcef- 

 laneoiis remarks ; i. DirecJ and reverfe fpeclra at 

 the fame time. Afpeflral halo. Rule to predeter- 

 mine the colours of fpeflra. 2. Variation of fpeftra 

 from extraneous light. 3. Variation of fpeflra in 

 number, figure, and remij/ion. 4. Circulation of 

 the b/oo i in the eye is vijtble. 5. A new way of mag- 

 nifying objects. Conclufion. 



WHEN any one has long and attentively looked 

 at a bright object, as at the fetting fun, on cloiing 

 his eyes, or removing them, an image, which re- 

 fembles in form the objeft he was attending to, 

 continues fome time to be vifible ; this appearance- 

 in the eye we fhall call the ocular fpe&rum of that 

 objetl. 



Thefc ocular fpe6^ra are of four kinds : ift, Such 

 as are owing to a lefs fenfibility of a defined pare 

 of the retina ; or fpeflra from defeB of fenfibility. 

 zd, Such as are owing to a greater fenfibility of a 



R r 2 defined 



