One of the most useful new features in the volume is the emphasis on flame photometry and fluorimetry. The improvements in burners and the use of photomultiplier tubes have greatly increased the sensitivity of these instruments. However, the general principles of these improved methods would have been helpful as a separate chapter, but they are likely to appear in a supplement. The text may be confusing because it recommends different burners for different elements, depending on the concentration of interfering elements and the choice of internal standards. While internal standards are desirable, their use can be problematic because the optimal burner temperature for a test element may differ from that of the standard. The book also describes fluorimetry as a useful alternative for determining lithium, with high sensitivity even in the presence of sodium and potassium. Volume 2A contains a large amount of new material, making it essential to the original four-volume treatise. The references are carefully selected from a wide range of scientific journals, without favoring American work. The book on statistical methods is well-written, explaining the main principles of statistical techniques. It is suitable for schools and universities, with clear explanations and exercises, though the absence of answers limits its usefulness. The book on perception and learning is a comprehensive text on behavior, covering topics from reflexes to reasoning, with a focus on perception, motivation, and learning. While the author's views are eclectic, the book provides a useful overview of experimental material and theories of learning. However, the lack of a clear theoretical framework may limit its effectiveness as a scientific discipline.One of the most useful new features in the volume is the emphasis on flame photometry and fluorimetry. The improvements in burners and the use of photomultiplier tubes have greatly increased the sensitivity of these instruments. However, the general principles of these improved methods would have been helpful as a separate chapter, but they are likely to appear in a supplement. The text may be confusing because it recommends different burners for different elements, depending on the concentration of interfering elements and the choice of internal standards. While internal standards are desirable, their use can be problematic because the optimal burner temperature for a test element may differ from that of the standard. The book also describes fluorimetry as a useful alternative for determining lithium, with high sensitivity even in the presence of sodium and potassium. Volume 2A contains a large amount of new material, making it essential to the original four-volume treatise. The references are carefully selected from a wide range of scientific journals, without favoring American work. The book on statistical methods is well-written, explaining the main principles of statistical techniques. It is suitable for schools and universities, with clear explanations and exercises, though the absence of answers limits its usefulness. The book on perception and learning is a comprehensive text on behavior, covering topics from reflexes to reasoning, with a focus on perception, motivation, and learning. While the author's views are eclectic, the book provides a useful overview of experimental material and theories of learning. However, the lack of a clear theoretical framework may limit its effectiveness as a scientific discipline.