In the development of an artesian basin this question is of the utmost importance; only by a knowledge of the static head and the ground-level can we, with any likelihood of success, estimate beforehand the discharge to be looked for in any particular district. If, for instance, we sink a bore in a locality whose surface is above the static head, the result, so far as a flowing well is concerned, can only be failure, however great the amount of water existing in the underlying strata. If a sufficient number of observations are available, it is possible to construct charts showing the isopotential lines, or lines of equal pressure, and these may be of great value when boring is contemplated in intermediate districts. It is seldom that accurate records of bores are preserved in the initial stages of the development of new artesian basins, and to this neglect is due much of the doubt which frequently arises at a later period as to the extent and permanence of the underground water-supplies. [Illustration: BORE NO. 5.] [Illustration: BORE NO. 14.] In some countries, however, the water-resources have long been the subject of exhaustive examination, notably in the United States, where a most valuable and instructive series of water-supply reports has been issued by the Geological Survey. The chief difficulties arise from the fact that bores are generally the property of private individuals, who are seldom both able and willing to supply accurate information. Discharges, for instance, are usually given in the roundest of figures, and without regard to the conditions under which they were taken. In Australia more than one geologist has called attention to the matter, and quite recently Mr. G. H. Knibbs, F.R.A.S., of the University of Sydney, in a valuable and suggestive paper on the hydraulic aspect of the artesian problem, refers to the want of comprehensive and deliberate investigation in the past, and admits the inadequacy of the available data for the determination even of the one question only—_i.e._, the extent to which exploitation can be pushed without fear of exhausting the supply. When drilling was first commenced in the Headquarters area, the bores were placed at an average distance apart of 500 metres; circumstances, however, led to there being a considerable variation in the depths of the wells, with the result that those of shallow depth and those situated on comparatively high ground were adversely affected by the deeper and more favourably placed bores. The sensitiveness of any one well to the influence of its neighbours is, I believe, far greater than is generally supposed, and appears to be especially dependent on the amount of difference between the depths, discharges, and surface-levels of the bores. In investigating this subject I made a number of experiments with the object of determining the mutual influence of wells, and perhaps some reference to these may not be without interest and value.