OR COLOUR BLINDNESS. 187 
12. That several of them are not sensible to the least refran- 
gible rays. 
13. That they see, as we do, the lines in the spectrum dis- 
covered by Fraunhofer, consequently the limits of brightness 
and of interior obscurity of the spectrum. 
14. That they do not judge as we do of the contrast of colours. 
15. That their affection does not proceed from a vicious con- 
formation of the eye, nor from any coloration of the humours of 
the retina. 
16, That the state of daltonism may be altered by means 
easily employed. 
17. That it has its origin in a defect of the sensorium. 
