GNR Hornsey Pegging Block

Great Northern Railway mahogany cased pegging block instrument. Removed from Hornsey No1 box 24/12/1974.

Uncle Google tells me the following:

Absolute Block is a method of working for use mainly on double or multiple track railways where each line normally carries traffic in one defined direction. The running lines are divided into block sections, each of which may only be occupied by one train at a time.

The signal boxes ('block posts') at opposite ends of a block section are equipped with block instruments, linked by electric line wires. The block instruments give both signalmen a continuous indication of the state of the block section.

The indicators are either of the 'pegging' or 'non-pegging' type. A pegging indicator (or 'pegger'), situated at the exit end of the section to which it applies, has an associated commutator handle. Turning the commutator alters the pegging indicator of that instrument, as well the non-pegger at the entrance end of the section. The pegger and the non-pegger connected to the same adjacent block post are normally combined into one instrument, which shows the state of both block sections on the two adjacent running lines. The non-pegger is placed above the pegger in a combined instrument.

Until the 1870s, block instruments generally had commutators and indicators with just two positions, labelled "Line Clear" and "Train on Line" (or "Train Entered Section").