-^298 Prof. J. Joly on a 



photopic vision will be shifted towards the red end of the 

 spectrum. This, according to the present theory, is the 

 explanation of why the photopic luminosity curve does not 

 quite coincide with the scotopic luminosity curve ; the 

 maximum of the first being at D, nearly, and that of the 

 •second being at E (Abney, Colour Vision, p. 103). 

 Working from these wave-lengths it is easy to show that the 

 electron must lose about 03 x 10 ~ 12 erg in penetrating 

 -the sheath ; L e.. almost 10 per cent, of its energy. It is, 

 according to the Quantum Theory, quite unnecessary to seek 

 for any other sensitiser than rhodopsin as the basis of vision. 



(10) It is probable, according to the present views, that 

 both rods and cones functionate by transmitting electrons 

 from the sensitiser into the optic nerve. The observed current 

 from fundus to cornea attending the light-stimulation of the 

 excised eye finds explanation in the present theory. Bayliss 

 (loc. cit. p. 522) reviewing the researches of Waller, 

 Einthoven and Jolly, and others, says : — " Respecting the 

 results of these researches the main fact is that, in the 

 uninjured eye of the vertebrate, the incidence of light causes 

 an electrical change in such a direction that the nervous 

 layer of the retina becomes electrically positive to the rod 

 and cone layer." It will be seen that this points to the 

 liberation of free negative electricity in rods and cones 

 attending the light stimulus ; i. e., to the presence of free 

 electrons in these terminal organs. 



(11) Chemical effects have been observed as taking place 

 in the retina when adaptation is changed from dark to light: 

 i. e., there is a change from alkalinity to acidity. This may 

 be involved in the loss of an electron by the ion HO and 

 the formation of the ion H + . 



(12) The movement of the cones attending light stimulus, 

 which in the case of most animals certainly occurs, and 

 which occurs in the case of Man, may be a mechanism 

 designed to bring the cones into un-exhausted sensitiser ; 

 the bleaching of the immediate layer touching the cone 

 being fatal to its full and proper activity. The rods carrying 

 the sensitiser within would not profit by such a move- 

 ment, and accordingly do not exhibit it. 



(13) Mechanical effects, such as pressure, appear to 

 liberate electrons and produce the latent image on a photo- 

 graphic plate. The luminous sensation attending pressure 

 of the eye-ball may arise in the same way : i. e., by the 

 mechanical liberation of electrons. It can be referred to 

 what is known as triboluminescence. 



(11) The degree of spectral analysis attainable according 



