The Clinophone, an instrument devised by the writer several years ago, was introduced for surveying boreholes, and, in particular, the boreholes used in the freezing process of sinking shafts through heavily-watered or “running” strata. It has recently been employed in this connection at the new sinking at Seaham Harbour, Co. Durham. The freezing holes are drilled round the shaft, and each contains tubes conveying the cold solution which forms the protective ice-wall. The holes must be as vertical as possible. There is, indeed, no other application of the art of boring in which such precision in drilling is needed and where so small a maximum of deviation from the vertical has to be stipulated. An essential to success with the freezing process is that each of the boreholes be accurately surveyed so that its path becomes known from top to bottom.