. The microscope and its revelations. is known us • opticians grease and an over-tightening of thepinion, driving its teeth into the rack, which, of course, speedilyends in disaster. If we desire to practically test this part of a microscope, wemust remove the pinion, take out the bar. clean off the opticiansCrease with petroleum from both bar and groove, oil with watch-makers oil, and replace the bar in the groove, and before refixingthe pinion see if it slides smoothly and without lateral shake. What has been said about the springing of the bar in this specialinstance applies equally to all
. The microscope and its revelations. is known us • opticians grease and an over-tightening of thepinion, driving its teeth into the rack, which, of course, speedilyends in disaster. If we desire to practically test this part of a microscope, wemust remove the pinion, take out the bar. clean off the opticiansCrease with petroleum from both bar and groove, oil with watch-makers oil, and replace the bar in the groove, and before refixingthe pinion see if it slides smoothly and without lateral shake. What has been said about the springing of the bar in this specialinstance applies equally to all moving parts, in stage and sub-stagemovements, .-aid wherever constant friction is incurred: equallyapplicable, too, is the suggest. lubricant weAn instrument leftunused in its native grease for twelvemonths becomes so im-mobile in most of it>parts by the hardeningof its normal lubri-cant that motion be-ci niies a peril to its futureif persisted in in thatcondition. If a coarse adjust-ment be what it sin midbe. all lower powers. FIG. 124A.—Nelsons stepped rack, invented in 1899. should be exclusively and perfectly focussed by it. and with thehighest powers objects should be found and focussed up to the pointof clear visibility. The exceedingly useful method of diagonal rack and twistedpinion was introduced by Messrs. Swift and Sou about 1880 andhas since been universally adopted. Its mode of operation is seenin fig. .124, a sectional drawing of this part of one of Swifts micro-scopes. The advantages gained by this method are due to the twistin the pinion being a shade steeper than the diagonal of the rack, bywhich expedient there is more gearing contact between rack andpinion, which prevents loss of time and obviates the necessity forunduly forcing the teeth of this pinion into those of the rack. Mr. Xelsoii has had made by Messrs. Watson and Sons a stillbetter form of rackwork. It is what is called a stepped rack (notof the diagonal, but of the straight type). In this v
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
