IN the Transactions of the Australasian Institute of Mining Engineers (Paper 136, vol. X.) some little time back there appeared, under the name of the present writer, an article on "-Concentration of Silver-Lead Ores." Since that article appeared the mill designed for the Block 10 'Company of Broken Hill, N.S.W., by Mr. J. 0. Armstrong, has been in daily operation, and has given excellent opportunities for the observation of power consumption. As the heavier parts of the machinery are driven by separate electro motors, each of which is fitted with a dead beat ampere meter, better opportunities are given for noting the power being absorbed than is the case with machinery belt-driven from one main engine. Before going into a further description of the mill it would perhaps be as well to give details of the electric power plant from which the mill motors obtain their current supply; but, as this paper is intended more particularly for the information of mining students, many details; descriptions, and illustrations are given which will not be of any great interest to engineers of experience.