The compilation of data on fissile isotopes is likely to increase rapidly, making the compiler's task more difficult. Including the method of measurement in tables and graphs is recommended, as a simple coding system is possible. A supplement to the compilation, which includes data from all sources on fissile isotopes, was not attached to the present publication. This supplement is valuable for those interested in atomic energy. The book, including the supplement, is available from the Government Printing Office. This well-presented compilation is as essential as its predecessors for those working with neutrons. The second edition of "Introduction to Mathematical Statistics" by Prof. Paul G. Hoel is one of the best undergraduate-level textbooks on theoretical statistics. It has been revised, extended, and greatly improved. It is suitable for first-year students with knowledge of elementary calculus and some familiarity with statistical methods. The book introduces probability before frequency distributions, which may seem counterintuitive but is beneficial from a teaching perspective. The book covers a wide range of topics, including frequency distributions, sampling theory, correlation, and regression. The treatment is clear and fresh, with enough exercises to help students master the techniques. Suggestions for future editions include using "theoretical statistics" instead of "mathematical statistics" and including topics like the algebra of expectations and generating functions. "Theodore Roosevelt as Naturalist" is a collection of Roosevelt's writings, highlighting his love for nature and his experiences in the Bad Lands and Brazil. The book provides a vivid account of life on a cattle ranch and his adventures with cowboys and "bad men." However, the book is marred by misprints and a poorly written introduction. The book is well-illustrated but has some issues with its content.The compilation of data on fissile isotopes is likely to increase rapidly, making the compiler's task more difficult. Including the method of measurement in tables and graphs is recommended, as a simple coding system is possible. A supplement to the compilation, which includes data from all sources on fissile isotopes, was not attached to the present publication. This supplement is valuable for those interested in atomic energy. The book, including the supplement, is available from the Government Printing Office. This well-presented compilation is as essential as its predecessors for those working with neutrons. The second edition of "Introduction to Mathematical Statistics" by Prof. Paul G. Hoel is one of the best undergraduate-level textbooks on theoretical statistics. It has been revised, extended, and greatly improved. It is suitable for first-year students with knowledge of elementary calculus and some familiarity with statistical methods. The book introduces probability before frequency distributions, which may seem counterintuitive but is beneficial from a teaching perspective. The book covers a wide range of topics, including frequency distributions, sampling theory, correlation, and regression. The treatment is clear and fresh, with enough exercises to help students master the techniques. Suggestions for future editions include using "theoretical statistics" instead of "mathematical statistics" and including topics like the algebra of expectations and generating functions. "Theodore Roosevelt as Naturalist" is a collection of Roosevelt's writings, highlighting his love for nature and his experiences in the Bad Lands and Brazil. The book provides a vivid account of life on a cattle ranch and his adventures with cowboys and "bad men." However, the book is marred by misprints and a poorly written introduction. The book is well-illustrated but has some issues with its content.