Excerpt from Minutes of Proceedings of the Institution of Civil Engineers, Vol. 36: With Abstracts of the Discussions, Session 1872-73 Part 2 An air-buffer at the back of the percussion cylinder has been introduced, with great advantage. The strong spiral spring K (vol. Xxiii., Plate for pushing forward the catches q', has been suppressed, and substituted in more recent machines by a new arrangement (plate 10, Fig. 3, T) by which the air, acting on a small piston, performs the same office. The rotation of the borer, formerly effected by the turning of a square arbor in the piston, is now performed at the end of the frame, near the face of the rock, where the torsion is much less. The machine as a whole is better balanced, and the repairs required have considerably diminished of late years. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.