. The microscope and its revelations. k ;and the fact that they areso placed as not to inter-fere with the stage, makesthis arrangement of dia-phragms ,-ind .stops an excellent one. and it is not clear why it has fallen into disuse. It had been thecnst to recommend the of this instrument racked <-////o- ,i-illii,i in- trtlltaiit if.* foCliS. Carpenter employed itu it hoi it, and (Bucket t within, and one or other of These met hods wasgeneral. Put in the use of good achromatic condensers with highpower work it soon became manifest to practical workers that it isonly when, as Sir David M
. The microscope and its revelations. k ;and the fact that they areso placed as not to inter-fere with the stage, makesthis arrangement of dia-phragms ,-ind .stops an excellent one. and it is not clear why it has fallen into disuse. It had been thecnst to recommend the of this instrument racked <-////o- ,i-illii,i in- trtlltaiit if.* foCliS. Carpenter employed itu it hoi it, and (Bucket t within, and one or other of These met hods wasgeneral. Put in the use of good achromatic condensers with highpower work it soon became manifest to practical workers that it isonly when, as Sir David Mrewster pointed out, the source i/i to be obtained. And .Mr. Nelson readily del istrated this fact even with the condenser dillett had devised. Ill next condenser of any moment is a most valuable one. andt it ilies one of t he great modern improvements of the microscope. I was an achromatic condenser of !7c devised and manufactured. I -Joli.—(lillctts condenser, fromon tin- Microscope. POWELL AND LEALANDS CONDENSER 301 by Messrs. Powell and Lealand. We have used this instrument forthirty-five years on every variety of subject, and we do not hesitateto affirm that for general and ordinary critical work it is still un-surpassed. Fig. 240 illustrates this apparatus. The optical com-bination is a 1th of an inch power, and it is therefore more suitablefor objectives from a ^-th of an inch and upwards; but by removingthe front lens it may be used with objectives as low as one inch. Having given to this condenser so high a place amongst eventhose of our immediate times, it may be well to specify what therequirements are which a condenser employed in critical work withhigh [lowers should meet. It is needful that we should be able(1) to obtain at will the largest solid cone of light devoid ofspherical Directly spherical aberration makes itselfapparent the condenser fails ; that is, when, on account of u
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
