Under the mechanics of the process fall the _sensory_, _motor_, and to a great extent the _perceptual_, elements in reading. _The sensory elements_ include the participation of eye, ear, and muscles as sense organs, furnishing respectively the visual, auditory, and kinæsthetic contributions to the total function. In the case of the blind, tactual sensations replace the visual, and in the deaf, the visual replace the auditory. Sensory impairment, that is, impairment of eye, ear, or muscle as an organ, may prevent an intelligent child from learning to read. Examination of the special senses is the first step dictated by common sense and scientific procedure, when an intelligent child does not learn to read. In this way it has happened historically that the first cases of special disability in reading and spelling among school children have been reported by ophthalmologists, to whom they were taken for examination of the eyes. Parents naturally sought the expert who knows eyes in such cases, for to one who has not studied the psychology of reading, it appears that a person “reads with his eyes” only. The _visual defects_ which may most commonly interfere with the mastery of the mechanics of reading are myopia, hyperopia, astigmatism, cataract, muscle-weakness, diplopia, and anomalies of the retina. Surveys of school children by competent oculists have shown that considerable numbers suffer from eye-defects sufficient to cause difficulty. _Deafness_ obviously may constitute an interference, since the correct sound of the word is essential to reading. Not so obvious is the rôle of the _kinæsthetic sensations_, but we are led to believe that their part is important through the studies of Fernald, later to be reported here. Under the motor elements involved, we have to consider _articulation_, _pronunciation_, _eye-movements_, and the _coördination of arm, hand, and fingers_ in writing words. It is hard for an expert reader, like an educated adult, to realize without first-hand study of the facts, to what extent these elements originally entered into his learning. The inexpert reader tends to retain lip-movements, and, indeed, movements of the whole apparatus of articulation, in silent reading. Perception of a stimulus may be defined for our purposes as seeing, hearing, or otherwise interpreting it in a certain way. Perception is habit, learned just as other habits are learned. We perceive the spoken words “home again” as such, because we learned to do so. One who has not learned, will not perceive two words, but only a jumble of articulate sound. In reading, the _perceptual elements_ include the formulation of habits of responding to parts, and to groups of words, as such. Many investigations have been made of the perceptual elements in the mechanics of reading within the past twenty years.