The excitement aroused by the publication of Haeckel's "Riddle of the Universe," and the many replies to the same, has in a great measure subsided, but the following letter from Professor Alfred Russel Wallace with reference to one of the most recent criticisms of Haeckel's theories will be read with interest by many. The book referred to is "Root Principles in Rational and Spiritual Things," by the Rev. Thomas Child (H. R. Allenson, 1905), and is a presentation of Swedenborg's doctrine of the origin of things as an antidote to Haeckel's materialistic theories. The brilliant author died not long after the publication of this book. Dr. Wallace writes:--

     "I have read so many books that attempt the solution of the deepest problems of the universe and fail that I always approach a new one without any expectation of enlightenment.

     "But I very soon found that I had at last in Mr. Child met with a man who had thought deeply, who could reason logically, and, perhaps most important of all, could express his ideas in clear and forcible language, and arrange his whole essay in the form of a compact and continuous argument and illustration.

     "In the form of a criticism of Haeckel, it expounds a new and very remarkable view of all the great ideas and principles which underlie the universe of man.

     "So far as I know, it is the most complete and satisfactory theory of the nature of matter and of mind, of force and life, of spirit, immortality, and freewill, that has yet been given to the world, and I thank you for making me acquainted with it.

     "As a criticism of Haeckel it is crushing, but it would receive more attention if it were issued in more expensive form as an independent exposition of 'Root principles,' and omitting altogether the last three chapters, which might be published separately, with some other passages from the book, as a criticism of Haeckel.

     "Who is Mr. Child? Do you know him? He is a thinker and reasoner of the very first rank. The only man who has made any approach to him in an equally forcible, but somewhat different way, is the late Mr. Arthur John Bell in his two fine works--'Whence Comes Man?' and 'Why Does Man Exist?' (1890).