The title refers to a magnifying glass that Jeb, the fifteen year old hero, gives to an Indian boy who is afraid to use it for fear that in melting snow with it he will be responsible for making the spring come a moment too soon. It's a story of growing up in mid-nineteenth century America and Jeb wants to rush the process of reaching a man's estate. He leaves his family and apprentices himself to Armand Deschute, a French fur trader reluctant to take the totally inexperienced boy into hostile Indian territory. Deschute is as moodily dedicated to justice and fair play as Batman (too good to read true), and the businessman and farmer who pay him as their guide West are stereotypes which nevertheless allow the authors to show the attitudes and habits of the time. When they are captured by Indians, Jeb's ability to learn fast (some excellent passages here on sign language) saves his scalp; some of the upside down virtues venerated by the Indian tribe provide Jeb with the contrasts that lead to mature insight. It's a rather slow book what with Armand and Jeb contemplating their navels as often as they do, but with the usual Johnson expertise in setting, character-building points and some excellent action passages.