400 Intelligence and Miscellaneous Articles. 



is recognized. Now we have found, in all our experiments, this 

 important fact, that the production of the initial luminous sensa- 

 tion requires, for the centre and all points of the rest of the retina, 

 the same minimum of the colour presented. 



This would seem to prove that the chromatic is a f auction dis- 

 tinct from the luminous sensation, both in its seat and in its nature. 

 Indeed we have seen that any luminous excitation whatever always 

 commences with producing a simple luminous sensation, while we 

 must always have an intenser excitation in order to get a sensation 

 of colour, — that the minimum of excitation necessary to produce 

 the luminous sensation is constant for the whole extent of the re- 

 tina, while the minimum of excitation necessary to produce chro- 

 matic sensations is by so much greater the more excentric the part 

 of the retina interrogated. 



These facts would be explained if it were admitted, as one of us 

 has sought to show in a previous work*, that the colour-sensations 

 are, in great part, the result of a special elaboration, made by the 

 nervous centres, of the impressions transmitted to them by the 

 retina — an elaboration which only comes after the simple primitive 

 sensation produced by any luminous excitation. For the parts of 

 the retina which we exercise the most, like that which corresponds 

 to the fixation-point, the intermediate phase which exists between 

 the simple luminous sensation and the consecutive chromatic ela- 

 boration is almost nothing, although it can be made evident by 

 certain methods ; while the less the retinal part put in action has 

 been exercised, which is the case for the excentric portions upon 

 which we do not ordinarily fix our attention, the slower and more 

 difficult to produce is the chromatic elaboration. 



As to the enormous imperfection of indirect vision, we have 

 previously proved that it affects solely the faculty of distinguishing 

 forms, which appears to be due to the following anatomical peculi- 

 arity : the centre of the retina receives, within an equal space, a 

 much greater quantity of nervous fibres than the excentric parts, 

 and consequently can convey to the brain a much greater number 

 of distinct impressions. — Comptes JRenclus de VAcademie des Sciences, 

 Feb. 18, 1878, tome lxxxvi. pp. 495-497. 



ON THE GALVANIC POLARIZATION OF PLATINUM IN WATER. 

 BY DR. FRANZ EXNER. 



The main conclusion drawn from the investigation refers to the 

 amount of the polarization called forth by currents whose electro- 

 motive force is too insignificant to produce persistent decomposition 

 of the water. For this hitherto virtually uninvestigated case the 

 law is deduced that the electromotive force of the polarization is 

 always exactly equal to that of the primary current. The paper 

 contains besides explanations respecting the causes which have 

 occasioned such varying values to be given by different authors for 

 the so-called maximum of polarization. — Kaiserliche Akademie der 

 Wissenschaften in Wien, math.-natunv. Classe, Feb. 28, 1878. 



* Charpentier, De la Vision avee les differ entes parties de la retine, 1877. 



