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SIR,-with reference to the letter from Mr. G. M. Frost, on page 166 of your March issue, may I be allowed to correct one of the figures given for the large Hyperbolic Cooling Towers erected from the designs of L. G. Mouchel and Parhers, for the Klip Station of the Victoria Falls and Transvaal Power Company? The diameter of each of the 5 towers now completed and of the 6th in course of erection, at base level, is 180ft., and not 100ft. The height given, viz., 220ft., is correct.
I CANNOT do better than introduce this short account of the San Francisco-Oakland Bay Bridge, by quoting the words of Governor Frank F. Merriam, Chairman of the California Toll Bridge Authority, in his preface to the First Annual Report on the progress of the scheme, issued on July lst, 1934. He there says:- "The end of the first year in the construction of the San Francisco-Oakland Bay Bridge has given the people of California visual evidence that the project which has dwelt in the minds of the people around San Francisco Bay for three-quarters of a century, but which many times had been declared by authorities to be an impossible dream. is now far advanced towards completion. Professor J. Husband
A brief description of the flow of coal from the pit to the user is as follows (see Figure 1):- Coal is mined in this country chiefly through vertical shafts with a few exceptions, where inclined drifts are used. The coal is brought to the surface in pit tubs, constructed either of timber or steel, and the full tubs are hoisted to the heapstead level, which is usually raised about 30 ft. above the general ground level. After leaving the cages, the tubs run by gravity to rotary tipplers, where the coal is tipped on to the classifying screens. These screens extract the coal below about 3 ins., termed "smalls" or "slack," and this is taken by belt conveyor to the cleaning plant, or loaded into wagons. The large coal passes on to the picking belts, where the dirt or shale is picked out by hand .and the clean coal delivered into railway wagons. The small coal, which is taken to the coal washing plant, is delivered into a raw coal balancing bunker from which it is elevated to the washer box, where the dirt or shale is extracted, and the clean coal passed on to the classifying screens, from which it is delivered into storage bunkers for the various sizes, or, alternatively, on to loading belts for delivery into railway wagons. The dirt which is extracted from the picking tables and in the cleaning process is taken to a dirt bunker and disposed of by ropeway, or other suitable means. The fines which are extracted in the washing process are used for boiler fuel or for coking. G.P. Bridges