My favorite orchestration book! The strengths of this book are its abilities to delve into the psychology of the players of all of the various orchestral instruments and by extension, the "soul" of each instrument, and, in its very British way, to charm the reader with colorful turns of phrase. To my taste, it is the least dry presentation of the subject of orchestration (which has the potential of being deathly boring.) I often enjoy picking up this book and re-reading it while sipping some tea or a hot toddy.
This is apparently a classic text on the subject - it's very fun to read, because it's somewhat outdated and somewhat UK-centric, but in an entertaining way. He's very thorough about what works and what doesn't for each instrument, and how best to use different techniques in different situations.