As regards Sensation, we are incessantly solicited by a variety of agencies, outward and inward. We may be roused into consciousness, through the eye, through the ear, through the touch, through the taste, through the smell, through the organic sensibilities; and all this at the same time with the rise of emotions or ideas through purely mental causes. Nay more; even under a single sense, we may have a plurality of distinguishable impressions. Sight is the greatest example. Hearing is little inferior; witness the complexity of a band of music, and the tumult of a stormy sea. In Touch, likewise, we may have a plurality of distinguishable feelings of contact over the body. The point to be considered, then, is, how many of these multitudinous effects, strictly synchronous in their occurrence, are capable of operating synchronously, either in directing the thoughts, or in impressing the memory. How many of them are able to work the smallest assignable change upon the consciousness? To all appearance, more than one at a time. Consider first the two senses most concerned in developing (out of muscular feeling as the basis) the notion of Space or Extension; that is, Touch and Sight. It will be enough to comment upon Sight. The eye, as is known, takes in a wide prospect; the retinas of the two eyes combined can embrace a large fraction of the surrounding visible sphere. Now, the attention at any one moment is confined to a limited portion: the precise limits are not here considered; there being a complication of action with sensation proper, which will be adverted to afterwards. But, notwithstanding this confinement of the attention, there is a consciousness of the whole visible expanse; as is proved in the case of any sudden change at any part; the attention is then instantly diverted to that part. We might say that there is, at every moment, a ramified area of sensibility, at its maximum in the centre--the line of direction of the eyes, and decreasing to the extremity or circumference of the visible expanse. To one gazing at the heavens, the flash of a meteor would be felt throughout the whole area of visibility; while it would be more certain in its effect, the nearer it was to the line of perfect vision, which is the place of special attention. A faint corruscation arising near the circumference might pass unheeded.