Tape recording of mine shaft signals

The recording of bell signals is not new. It was done on the Karlick tachograph by means of inking pens. Then magnetic recording was tried some years ago but wire was used as the recording medium and this was too bulky for satisfactory storage. The inking pens were re-introduced some years later and records are still being made on a narrow paper tape. Experiments were then carried out with a magnetic tape recorder to find out if it was feasible to use this type of recorder—and to find out some of the difficulties.