Four more on metrics, and all are adequate introductions to the system though not all measure up to last year's batch. (See KR, 1974, p. 641, J-273.) Ross, in textbook prose that makes his book less readable than it looks (or than Donovan's more extensive 1974 one reads), surveys the history of weights and measures from prehistoric times, with special chapters on the metric and the ""hodgepodge"" English system and the controversy between them in the United States, where, he concludes, metrics must be adopted if only so we can compete in world markets. Specific refinements and units established by the International Bureau are explained and a glossary, tables and conversion charts appended. Lamm's history is easier, even conversational, and she follows it with a patient guide through comparative measures and metric units, urging readers to ""think metric"" directly but appending, for the transition, a table of conversions for the more commonly used measures. No intricacies here but Lamm could help children feel at home with the new measurements. Schlein, who supplies more tables, also emphasizes ""thinking metric"" and explains at an even younger level how the system works, why it is simpler to use than ours, and how it can he inconvenient to be the only people using other units. Finally, Branley really practices the directive he used first (his Think Metric, KR, 1973, led the rest by a year or two), showing children how to make a meter stick, balance, and liter box, then measure themselves and common household objects and weigh smaller items, without once mentioning conventional units. With Lustig's brightly amusing comic-art pictures, it makes an excellent beginning, especially for children who haven't yet become accustomed to inches and ounces.