THE TELEGRAPH AND THE ABSOLUTE BLOCK: SINGLE LINE OPERATION is the second volume in the series titled “The History and Development of Railway Signalling in the British Isles”.
 
This volume is in two parts. Firstly, the electric telegraph was vital to the early operation of railways. Needle telegraphs developed in time to the use of telephones. Telegraph working developed into block working with the wide range of instruments to support the systems. Described in detail, some of these instruments remain in use today. In the second part, it is shown how control of single line working has always been important for obvious reasons to avoid collisions. The many systems used to control single line working are covered in detail. Working with and without tokens, instruments, train staffs, electric and radio electronic token block are all amply discussed.