The inquiring junior scientist (and most families produce at least one) will find the answers to endless questions in the amazingly comprehensive book about the kinds of ""machines"" all of us encounter repeatedly. In every home there are dozens of them, from oil cans and fountain pens, through vacuum sweepers, pressure cookers, electric lights, clocks, and washing machines. Just outside the door there are skates and bicycles, lawn and tools. Even musical instruments classify as ""machines"" here. The grouping of various devices is skilfully designed to carry over basic principles of operation, and as presented with clarity, precision, and exactness, it seems simple even to those of us who-like Nina- are distrustful of machines. This is not a volume in the Let's Find Out series of first science books which the Schneiders have written jointly, but it is a next step up the ladder of everyday science, with simple experiments to help reenforce the scientific approach. The factual illustrations (by Jeanne Bendick) are, on the whole, satisfactory; we wish she didn't feel she had to introduce human figures which are detrimental to the appearance of the book. A sure favorite for a large audience of budding scientists, even those who may never go farther than changing a bicycle tire; and a must for school libraries.