To transfer the meridian underground is the fundamental problem in mine surveying, yet it is usually treated very inadequately in text-books. The following paper is concerned with one of the methods-namely, by means of two wires in one shaft. The first part of the paper is descriptive of the general procedure, but is far from exhaustive, since considerable space is required for discussing the theory of the subject. When it has seemed necessary to choose between appearing somewhat dogmatic and discussing a point at great length, the former alternative has been chosen, in the interest of clearness and conciseness. In general, the conditions supposed are those of the ordinary Australian or Western American metal mine. The second part of the paper contains a development of the theory of Weisbach's method, in which the instrument is set nearly in line with the wires, and, incidentally, of the particular and common case in which the instrument is set exactly in line. The third part contains a development of the theory of Weiss's method, in which two instrument positions are used. The writer has been unable to find any discussion of this method, which is not mentioned in most books, while Weisbach's method rarely gets more than casual treatment.