MESSRS. EDITORS—I am very well acquainted with a man whose ears are not mates— they are not in unison—both being tuned to a different key ; still, in regard to hearing at a distance, they are both alike. But when a certain key is touched on the piano, (say the note A,) he is able to give the same sound with his voice, if he listens only with his left ear. If he closes the left ear, and listens only with his right ear, he cannot give the note, A, as before, but another, the note G—one degree of the musical staff below A. If the above statement of the case be correct, how can he listen to music with any degree of pleasure? It may be said that he cannot, one ear being tuned to the key of A, and the other to the key of G—A and G being consecutive notes—he would, of course, hear discords. The argument seems to be a plausible one. I am aware that a similar case has been recorded of a man who could listen to music only with feelings of horror. One ear was tuned to the key of A, the other to the key of G. But it is not true that the man in the other case is horrified with strains of music ; nothing more agreeably arrests his attention than good music. Can the SCIENTIFIC AMERICAN show why good music affected one man so unpleasantly, while it produces in the mind of the other feelings of pleasure ? T. D. I. Monroe, Mich., May, 1858. [The most curious phenomena connected with this case is not that regarding which our correspondent interrogates us, but that whereby the person alluded to hear* a tune played on the same key with both ears, at a distance, but different keys (A and G) when adjacent to the performer. Some mistake must have been made in the observations of the person alluded to, as he undoubtedly would hear nothing but discord if one ear were tuned to G, and the other to A. If the ears were tuned to the difference of a third or a fifth in the musical scale, harmony, of course, would be produced, but not to a second, such as between A and G.—EDS.