. The microscope and its revelations. e Institiit. Paris, made small achromatic lenses; but they weretoo imperfect in lie of real service. In 1811 Fraunhofer madeachromatic doublets with no great success; and in 1823-4 an achro-matic microscope was made by the Messrs. Chevalier, with fourdoublet lenses arranged according to a plan devised by • Microscope dEuler followed, and in 1827 Amid constructed ahori/.ontal micro-cope on achromatic principles, which was spoken well of. But whileup to a very recentdate it was commonto assert that the firstto suggest the planof combining two,
. The microscope and its revelations. e Institiit. Paris, made small achromatic lenses; but they weretoo imperfect in lie of real service. In 1811 Fraunhofer madeachromatic doublets with no great success; and in 1823-4 an achro-matic microscope was made by the Messrs. Chevalier, with fourdoublet lenses arranged according to a plan devised by • Microscope dEuler followed, and in 1827 Amid constructed ahori/.ontal micro-cope on achromatic principles, which was spoken well of. But whileup to a very recentdate it was commonto assert that the firstto suggest the planof combining two,thrive, oi four plano-convex achromaticdoublets of similarfoci, one above theother, to increase thepower and aperture,was Selliguein l«-j:!.it is now known thatthis had been antici-pated b\ Mar/oli ( 353). Selliguesplan was carried intoexecution 1 >y theMessrs. instrument embodvinir this plan is 115. In a report to theAcademic Royale desSciences, the well-known mathema-tician Fresnel says,c incerniny this mi-. shown in fig FIG. 115.—Selligues arhnmuitic microM-. .|M i 823 V llV^AAAAAAi^ I 1 11 ,-> Jill uscope. that in comparing the objectives with those of one of Adamss achromatic instruments that un to a magnification of up hundred times Selligues was decidedlythat superior ; but beyond magnification there was no superiority in the achromatic form.• preferred Adamss form for prolonged observations because••<• .-i larger lie],! i |l;m Selligues. chanism ,,( t|,js mici-oscope was similar the English shown ai tig. I \-2. The focussing was by rack and on the stage, the pinion travelling with the stage on 1 draw tubes A and 15. were applied within the t1 upper one having a biconcave lens. S, at the pee, , ls:;:i, ,,. 86. MODEL STANDS FOE ACHROMATIC OBJECTIVES I4Q lower end, serving as an amplifier, which was probably the firstapplication of a Barlow lens to ,-i microscope. Illumination for opaque objects was accomplished by a lent
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
