MR. JENNlNGS, who is the author of 'In London's Shadows,' has made an exhaustive and first-hand study of the vagrancy question. This summer he lived the life of a vagrant for a month, tramping the roads, sleeping in casual wards, and making the acquaintance of hundreds of ' down-and-outs.' No one, even in the casual wards where he slept, discovered his identity. He tramped for 300 miles, from spike ' to ' spike,' begging his food and doing odd jobs by the way. Mr. Jennings, who has become known as the 'Doss House Parson,' broadcast some two years ago on the subject of vagrancy in the East End. In his talk tonight he will describe some of his racy and illuminating experiences during his most recent tour of the underworld.