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turns, or working-places. We therefore propose to recommend a more workable and adequate standard for quality, quantity, and temperature of mine-air, and one which will fulfil the altered mining conditions of recent years without unduly harassing the mine-owners, but, on the contrary, may in some cases tend to reduce the cost of mining by providing a cooler and more invigorating aircurrent for those employed underground. A quantity standard alone {i.e., the anemometer measurement of the air), as now in operation, is subject to many practical difficulties, for the amount of air required for adequate ventilation varies according to the nature of the individual mine, and cannot be fixed at a given quantity per person at all mines alike, for the following reasons : — (a.) The variable temperature of different mines. One of the principal objects of ventilation in deep mines is the reduction of the temperature of the exposed rocks. If this were not effected the work would be unbearable. (b). The quantity of organic carbon-dioxide from men and animals is variable. (c.) The velocity of the air-current necessary to sweep away noxious gases and dust and to reduce the temperature of the rocks is dependent on the sectional area of the airways and stopes, and a specified quantity per person adequate for the confined stopes of the Thames Goldfield might be insufficient to create any observable current in the wide stopes at Waihi. (d.) An efficient distribution of the air-current and proper air-stop-pings, also brattice and doors, are necessary, otherwise a large quantity entering the mine may inadequately ventilate the workings. (<?.) The variable exudation of noxious gases from minerals and rocks, which varies in the same mine as the area of the exposed rocksurfaces. In the mines of the Hauraki Goldfield, more especially at Thames, a gaseous mixture of nitrogen and carbon-dioxide in new workings frequently emanates from fissures in the country rock and in the quartz veins, especially when northerly and easterly winds (the rain-bearing winds) prevail. The presence of these gases has been assigned to two different causes—viz., the action of acid on carbonates such as calcite, or to the dying exhalation of an extinct volcano. The following analysis of gas collected from a winze at Thames may be taken as fairly representative :- — Oxygen ... ... ... ... ... ... .... B'2 f- Nitrogen ... ... ... ... ... ... ... 546 Carbon-dioxide ... ... ... ... ... ... 37"2 100-0 The specific gravity relative to air was 119. The mine-gas is therefore equivalent to a mixture of 392 volumes of air, 372 volumes of nitrogen, and 236 volumes of carbon-dioxide. The presence of this gaseous mixture in certain of the mines is not only a source of considerable annoyance to miners, but has at times caused suspension of mining operations, and has been attended with loss of life. On this goldfield, generally speaking, the deeper the mine-workings the more abundant is the amount of gas present. On the occasion of our inspection of the low-level crosscut (1,000 ft.) to connect the Thames mines, now being driven in altered andesite country rock, we obtained further evidence of the impracticability of a uniform fixed quantity standard for all mines. At the face of the crosscut then being driven, near which was a fissure giving off water and gas, we obtained samples of mine-air. The place was ventilated by a 22 in. circular air-pipe connected with a Roots blower at the surface, which delivered 1,695 pubic feet of air per minute as near to the face as such pipe could be safely carried without destruction by blasting. Upon analysis the sample was found to contain 3-31 per cent, of CO 2 . Four men were working at or about this face, and the quantity of air per man per minute was 424 cubic feet. To dilute this CO 3 with pure air, so as to bring the