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 270 NEW BOOKS. his own experience there is a real causal agency, he cannot escape the conviction that it is in constant relation to a wider purpose of the same order of being, but free from his limitations. It is the aim of Dr. Lloyd Morgan to show that a belief in purpose as the causal reality of which nature is an expression is not inconsistent with the full acceptance of the explanations of naturalism within their appropriate sphere. He admits, nay, contends, that the existence of such a unifying agency is not a scientific conception : it is not a phenomenon though manifested by phenomena. It is, if you will, a postulate of reason, a regulative prin- ciple, as valid for rational thought as mechanism. Determinism is purpose finding expression in determinate sequence ; and, just because he believes that all that science discloses is the manifestation of a con- tinuous purpose, he believes that the manifestation is itself continuous, and the origin of life and mind ideally capable of explanation in terms of antecedence, co-existence and sequence. Both writers regard Life as a directive force, but while Dr. Lloyd Morgan, accepting the concomitance of the ideal constructions of physiology and psychology, sees no objection to an all-embracing mechanical interpretation, Sir Oliver Lodge asserts that no mechanical analysis can be complete and all-embracing. Guid- ance and control are not forms of energy, or phantom modes of force, and their superposition upon the scheme of physics need perturb physical and mechanical laws no whit. It is only necessary to recognise that the laws of physical science are incomplete, when regarded as a formulation and philosophical summary of the universe. Their determinateness is got by the sheer assumption that no undynamical or hyperdynamical agencies exist. For him Life and Mind are outside the scheme of mechanics. It is, moreover, simply untrue to say, as Haeckel does, that the modern physicist has grown so accustomed to the conservation of matter that he is unable to conceive the contrary. It is quite easy to conceive the identity of the electrons lost, so that the destruction and even the creation of matter are well within the range of scientific con- ception, and may be within the realm of experimental possibility (p. 33). Monism must not signify a limitation of mind to the potentialities of matter as we at present know it. In detail Dr. Lloyd Morgan is extremely interesting. He would re- strict the term " intelligence " to the guiding factor hi behaviour as the result of experience when it falls within what Dr. Stout calls the per- ceptual sphere. Just as the instinctive factor provides data which intelligence deals with so as to shape it to more adaptive ends, so does the perceptual factor provide the more complex data which, through ideational process, are raised to a yet higher level in rational conduct, where a situation is developed, not only in accordance with the impulse value arising therein, but also, and in a greater degree, in accordance with the motive worth for a system. And he argues that to this should correspond a further differentiation within the control system itself. The Tenth Division of his book in which this subject is discussed is particularly well worth reading. DAVID MORRISON. Optical Illusions of Reversible Perspective : A Volume of Historical and Experimental Researches. By J. E. W. WALLIN. Profusely illustrated. Published by the Author, Princeton, N.J., 1905. Pp. vi, 331. Price $1.85 (paper), $2.25 (cloth). The central portion of this book consists of a report of experiments on perspectivity in momentary exposures (with student observers) and on the