240 WRITINGS OF JOSEPH HENRY. [1845 



nothing about the sensorium or its connection with, or mode 

 of operation upon, the nerves of sensation ; and from the 

 analogy of sight and hearing he has no hesitation in pre- 

 dicting that there may be found persons whose color-blind- 

 ness is confined to one eye, or at least is greater in one eye 

 than in the other. " Nor is this (says he) wholl}'' a conjecture 

 from analogy, for my own right eye, though not a better one 

 than the left, which has no defect whatever, is more sensible 

 to red light than the left eye." The case is precisely anal- 

 ogous with respect to his ears, for certain sounds; and no 

 person, it is presumed, will maintain that there is a sensorium 

 for each ear and each eye. 



Whatever may be the cause of the inferiority, there exists 

 a very easy means of compensating it to a certain extent. 

 This method, first used by Dr. Seebeck, consists in viewing 

 colored objects through colored media. Suppose the medium 

 to be a piece of red glass; the impression of a red body and 

 a green one on the eye of a person like Dr. Dalton, 

 would be different, although with the naked eye they would 

 be the same. Tlie red glass would intercept much more of 

 the light of the green object than of the red one, and hence the 

 two would be readily distinguishable by a diiierence in the 

 intensity of the illumination of the two objects. Nothing 

 can equal the surprise, says Professor Wartmann, of a Dalton- 

 ian when the errors which he commits every day in the ap- 

 preciation of colors are thus disclosed to him. 



EXPERIMENTS ON ELECTRICAL DISCHARGE. 



(Proceedings of the American Philosophical Society, vol. iv, pages 208, 209.) 

 November 7, 1845. 



Professor Henry communicated the result of a series of ex- 

 periments on electricity made last winter. They had refer- 

 ence, first, to the discharge of electricit}'' through a long wire 

 connected with the earth at the farther end ; secondly, to the 

 discharge of a jar through a wire ; and, thirdly, to an 

 attempt to account for the phenomena of dynamic induction. 



He first showed that when a charge of electricity is given 



