Note 18 — Chapter II · PRACTICAL OPERATIONS AND DETAILS.
Reading edition
These numbers are for small shafts of about 2' by 4'; large shafts require a larger force. They advance at about the same rate as galleries of equal cross-section.
Reading edition
These numbers are for small shafts of about 2' by 4'; large shafts require a larger force. They advance at about the same rate as galleries of equal cross-section.