THE FOURTH DIMENSION 393 



have not now become public property. The following are some of the 

 works that he has consulted : " Non-Euclidean Geometry," by Henry P. 

 Manning; "The Elements of Non-Euclidean Geometry," by L. L. 

 Coolidge; "The Fourth Dimension Simply Explained — a collection of 

 Popular Essays with an Introduction and Editorial Notes by the Editor," 

 Henry P. Manning, editor (published by the Scientific American) ; 

 " The Fourth Dimension," by C. H. Hinton; " The Fourth Dimension," 

 in "Mathematical Essays and Eecreations," by Hermann Schubert, 

 translated by T. J. McCormack.] 



TOL. lxxxiii.— 27. 



