MAKING HELIOSTAT.
On the base (Fig. 786) is hinged at r a smaller base k which may be inclined and clamped at any angle up to about 60° with safety. The clamping is done by the thumbscrews h and the slotted brass bar g, which is in the form of a curve, having its centre at r. On k a fairly good American clock is clamped, and l is pierced to allow the clock to be wound from underneath. The hands are taken off, and on the hour axle is fitted the wooden cylinder c. The latter is furnished with an axle f (see Fig. 787) which bears in a hole in the brass arm j, c will make one rotation in 12 hours: from a groove, however, a band passes to the bigger pulley which has twice the dia meter of the grooved part of e. In con sequence, e will turn round once in 24 hours. The mirror is carried on a steel axle d which bears on a small metal plate screwed to 1:, and the pulley e is firmly fixed to this steel rod, which may be a stout knitting needle. On the axle d is
also soldered a small collar n for the arm j to press on sufficiently to prevent vibra tion. It will be seen from the plan that the mirror and its axle can be easily re moved for cleaning, etc., on raising up j, as it is only kept in position in the slot p by the band as, which may be indiarubber. The mirror, which presents its silvered surface to the sun, is held in a brass strip b, to which the axle a is soldered. The two brass straps c keep the axle stiffly in position. The frame o can be made of wood. The paint and varnish of the mirror are removed by paraffin oil and methylated spirits, and the quicksilver carefully polished by rouge, so that the ; back, or silvered side, can be used.