Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature . ich drawings of the scales have all been madewith the aid of Ross or Becks object-glasses andPowell and Lealands achromatic condenser (170°).The markings can be seen without an achromaticcondenser; but the view is infinitely more satis-factory when this apparatus is used. I have alsoemployed Smith and Becks, which is admirablyadapted for exhibiting them. A moderate apertureonly is requisite, both in the object-glass and theilluminating apparatus, for their perfect di
Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature . ich drawings of the scales have all been madewith the aid of Ross or Becks object-glasses andPowell and Lealands achromatic condenser (170°).The markings can be seen without an achromaticcondenser; but the view is infinitely more satis-factory when this apparatus is used. I have alsoemployed Smith and Becks, which is admirablyadapted for exhibiting them. A moderate apertureonly is requisite, both in the object-glass and theilluminating apparatus, for their perfect display; butthe workmanship of the objective must be of thebest description. Any error in the correction ofthe lenses, whether in the manufacture or in theiradjustment for penetrating the thin covering glass,is immediately betrayed by the peculiar appearancewhich the markings present. Mr. R. Beck hasdealt with this subject so thoroughly in the paper Ihave alluded to, that I hardly feel competent tospeak on it* I have seen the markings moderately * I refer more particularly to the accepted standard Fig. 50. SameScale, directillumination;TV objective,C eyepiece. Fig. 49. Scale of Speckled Podura, oblique illumination. An object-glass, which will show the Podura scaleperfectly, may be predicted to be capable of beingemployed satisfactorily on the easier diatoms, suchas P. angulata and P. hippocampus; but it doesnot follow that another glass, which will show thestriae on the N. rhomboides, Surirella, P. fasciola,N. cuspidata, &c, will perform equally well on thePodura scale. It is possible, however, for a goodhigh-power glass to be equal to both these require-ments. Amateur mounters should cover the scalesthey put up with the thinnest possible glass, so that,when opportunity offers for an examination of theslide under a remarkably good -^th or TVth, theymay not find themselves doomed to disappointment,owiug to the inability of the objective to penetratethe thick cover. I
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectscience
