THE SILENT CLOWNS is not specifically about Laurel and Hardy, but famed critic Walter Kerr did devote two chapters to them near the end of this excellent history of silent comedy.  His thoughts on how Laurel and Hardy transformed themselves and silent comedy are well worth reading and even memorizing.  While the major focus of THE SILENT CLOWNS is Charlie Chaplin and Buster Keaton, Kerr covers Lloyd and Langdon, as well as W.C. Fields, Raymond Griffith, Lloyd Hamilton and just about every comedian who ever stepped in front of a camera to do a pratfall.  The Laurel and Hardy chapters are superb on their own, but they really shine when read in the context of the entire history of silent comedy, meaning you should read the whole book.