. The microscope and its revelations. also a matter of importance, because when amicroscope is used for photomicrography it is essential that itshould have a body with a large diameter. III. Arrangements for focussing stand next in order of import-ance. Every microscope of the first class is provided with twoarrangements for focussing, one a coarse adjustment, acting rapidly,and the other -A fine adjustment, which should act with great delicacy l6o THE HISTORY AND DEVELOPMENT F THE MICROSCOPE |> A -nod coarse adjustment or primary movablepart ofthe instrument is of great impoi-tan
. The microscope and its revelations. also a matter of importance, because when amicroscope is used for photomicrography it is essential that itshould have a body with a large diameter. III. Arrangements for focussing stand next in order of import-ance. Every microscope of the first class is provided with twoarrangements for focussing, one a coarse adjustment, acting rapidly,and the other -A fine adjustment, which should act with great delicacy l6o THE HISTORY AND DEVELOPMENT F THE MICROSCOPE |> A -nod coarse adjustment or primary movablepart ofthe instrument is of great impoi-tance. The first requisite isthat tin- body or movable part should move easily, smoothly, hutuithoiit shake in the groove or sloi or whatever else it slides in.\Ye ha\r found in practice that a har shaped like a truncated prismsliding in a suitable groove acts best and longest. But a bar planedtrue and placed in a groove ploughed to suit, it is not enough. The this brino-s with it a fatal inevitable friction determines wear, and. Flu. 1-24.—Dia-onal rack and twisted pinion devised in 1881. All such grooves, which are usually «l,rnM be so thai by tightening upthe vs by s the bar or limb isagain firmly -rippi>d. Further, the tor its whole length along the groove but only fcher (11 ;l1111 » the middle. IWell introduced these - •>• arse adjustment more than 60 years •usands of instruments in which these principles applied , Keen, by sheer friction wear, soon •- since then! l!m instruments made bv ; ARRANGEMENTS 161 this firm are as good after thirty years use as they were when new. Frequently bad workmanship is concealed by the free employmentof what 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 petroleu
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
