Alexander Graham Bell autograph letter signed regarding ''visible speech'', the system created by Bell's father to help deaf individuals such as Bell's mother. Composed on ''Clarke Institution for Deaf Mutes'' letterhead on 6 March 1872, Bell writes to Charles Perkins, Secretary of the Social Science Association in Boston, offering to ''purchase two hundred copies of the article on Visible Speech''. In addition to his mother, Bell's wife was also deaf, and he dedicated much of his life to the advancement of those with hearing and speech disabilities, in addition, of course, to the pursuit of his inventions such as the telephone. Single page measures 5.25'' x 8.25''. Light toning, separation starting at top vertical fold, and minute smudging to signature. Overall in very good plus condition.