. Quarterly journal of microscopical science. ^F. H. Wenham. MEMORANDA. 201 Substitute for the Rack-and-Pinion movement of Microscopes—I have found the following application of the frictionalgearing (sometimes used in cotton-spinning machinery)answer perfectly well in lieu of the ordinary rack-and-pinionmovement of the body and stage of microscopes. It is quitefiee from the unpleasant drop consequent upon a worn rackand pinion, and is exceedingly strong, it being impossible toinjure or fracture the movement, by any undue violence, inturning the milled head, for beyond a certain amount of strai
. Quarterly journal of microscopical science. ^F. H. Wenham. MEMORANDA. 201 Substitute for the Rack-and-Pinion movement of Microscopes—I have found the following application of the frictionalgearing (sometimes used in cotton-spinning machinery)answer perfectly well in lieu of the ordinary rack-and-pinionmovement of the body and stage of microscopes. It is quitefiee from the unpleasant drop consequent upon a worn rackand pinion, and is exceedingly strong, it being impossible toinjure or fracture the movement, by any undue violence, inturning the milled head, for beyond a certain amount of strainit will slip. Fig. 1 is a plan and fig. 2 side view of a microscope bodywith this movement attached. The same letters of referenceapply to both figures ; a is the body of an ordinary microscope;b a strip of brass in the position of the usual rack—this isplaned out longitudinally into three or four angular furrows,slightly truncated, as shown; c is a turned cylinder of steelwith milled heads, in place of the pinion—this has furrows and. Fig. 1. Fig. 2. grooves of the same angle exactly corresponding with those ofthe strip. The pinion or roller is pressed into the strip by means ofa hammered brass spring (d), which serves to ensure a uniformpressure, needful to obtain sufficient bite between the rollerand strip, to overcome the resistance of the work, and alsogives accommodation to any irregularities of construction. The lifting power or bite depends upon the acuteness of theangle given to the ridges and furrows, which must not be tooobtuse, or not exceeding 30°. I have made a friction rack of this description which worksvery smoothly, and lifts a weight of 16 lbs. without slipping;this force is amply sufficient for most optical purposes.— Wen HAM. 202 MEMORANDA. Notes on Tricuspidaria and Pentastoma.—In the precedingnumber of this Journal (p. 115), a series of clearly definedvascular prolongations are described by me in connexion withthe calcareous corpuscles of
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