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80 Reid observes, the first attempt that ever was made to distinguish the immediate and natural objects of sight, from the conclusions which we have been accustomed from our infancy to draw from them. He draws a boundary between the senses of sight and touch; and he shews clearly, that the connection which we form in our minds between sight and touch, is the effect of habit; insomuch that a person born blind, and suddenly made to see, would be unable at first to foretel how the objects of sight would affect the sense of touch, or, indeed, whether they were tangible or not; and, until experience had taught him, he would not from sight receive any idea of distance, or of external space, but would imagine all objects to be in his eye, or rather in his mind. These, and other interesting positions, have since been completely verified by actual experiment, as may be seen more particularly in the case of a young man born blind, who, at the age of fourteen, was couched by Mr. Cheselden, in 1728, and received his sight. An account of his sensations and ideas is given in Cheselden's Anatomy; and has been considered sufficiently interesting to be transcribed into the works of numerous writers on the science of the human mind. In 1733 he published a "Vindication of the Theory of Vision."

In 1710 appeared "The Principles of Human Knowledge;" and in 1713, "Dialogues between Hylas and Philonous." But of these works we cannot speak with the same degree of praise: they are, indeed, one of the most astonishing proofs how far a strong and energetic mind may be carried away by the pursuit of an absurd and delusive theory. The object of both works is to prove, that the commonly received notions of the existence of matter are absolutely false; that there are no external objects, no world, or any thing in it; but that all things merely exist in the mind or ideas, and are nothing more than impressions produced there, by the immediate act of the Deity, according to certain rules termed laws of