The London, Edinburgh and Dublin philosophical magazine and journal of science . We should therefore put in a stopwhich will block out all beams thathave a grasp less than this *. Theimage at x will then have the ap-pearance represented on a large scalein the annexed diagram. An annulusof bright light will be seen in itbetween the edge of the stop, whichlies at ^/ = 071, and the limit ofthe grasp of the condenser at G^O85,and faint light will be seen farther out to the limit of thegrasp of the objective at G = l*25. We may, however, with advantage block out still more ofthe light. For the spec
The London, Edinburgh and Dublin philosophical magazine and journal of science . We should therefore put in a stopwhich will block out all beams thathave a grasp less than this *. Theimage at x will then have the ap-pearance represented on a large scalein the annexed diagram. An annulusof bright light will be seen in itbetween the edge of the stop, whichlies at ^/ = 071, and the limit ofthe grasp of the condenser at G^O85,and faint light will be seen farther out to the limit of thegrasp of the objective at G = l*25. We may, however, with advantage block out still more ofthe light. For the specks upon the diatom are numerous,and although not quite regularly disposed, they are approxi-mately in straight vertical rows, and less regularly in some-what wavy horizontal rows. In this description we suppose Image x, with X scale. A 0 o Z>o z o Oct 0 d o. * To get the stop accurately into its place it should be mountedso that it can be centred relatively to the condenser. Provision forthis adjustment is always useful and sometimes essential for accuratework ; and Messrs. Watson and Sons, at the request of the writer, madean adjustable cell for holding the stops which is entirely satisfactory. 510 Dr. G. J. Stoney on Microscopic Vision. the length of the diatom to be placed horizontally. Now thenearest of the diffraction-spectra which such sources of lightwould produce are disposed round a direct ray z, as in thefirst of the diagrams on p. 509. Accordingly, when z isin the neighbourhood of a of the second figure, it producesone, and only one, diffraction-spectrum, that at a, which comeswithin the grasp of the objective. Similarly the direct beamswhich have their puncta near V produce diffracted beamswith their puncta near b. And in the same way the beamswhich are concentrated into those puncta of image x which lienear c and d! will prod
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Keywords: ., bookcentury1800, bookdecade1840, bookidlondon, booksubjectscience
