An England cricket tour is a unique phenomenon, with its own pressures, challenges and remarkable highlights. It presents its participants - shorn of the usual support networks they enjoy at home - with a prolonged test of skill, physical stamina and mental resilience. Now Simon Wilde, author of the acclaimed England: The Biography, examines in The Tour the delicate chemistry that makes for a successful tour and why others disintegrate so badly.    Since the 19th century, England has been sending its cricket teams around the world to take on their rivals. Initially, these trips were undertaken by boat, meaning players could be away for many months, often in alien conditions. With air travel reducing journey time and facilities much improved, the challenges still remain: homesickness, isolation, hostile crowds - not to mention an opposition determined to win at all costs. For some, the experience can be too much, while others thrive in the heat and dust of battle.  The Tour looks at all aspects of the history of England's cricketers abroad, including the burden placed on the captain, who is expected to combine on-field acumen with the deft touch of an ambassador off it. There have been diplomatic incidents aplenty, from Douglas Jardine's Bodyline tactics to Len Hutton's tour of the Caribbean, as well as the special pressures of playing in countries such as India and Pakistan during periods of unrest. Touring has never lost its romance. There have been serious scrapes, from court cases to car crashes, but also much fun, whether joining in with the Barmy Army or David Gower famously taking a Tiger Moth for a spin. Wilde explains how this seemingly anachronistic activity has been adapted from an instrument of imperial soft power to a relentless cricket circus that never ends.   Simon Wilde has once again created a masterpiece of insight, information and entertainment, an aspect of cricketing life that few will ever forget: the tour.