Monthly microscopical journal: transactions of the Royal Microscopical Society, and record of histological research at home and abroad . ject-glass of 120°. Is all aperture beyond 120° then useless ?I next measured the Tolles ^th in the ordinary sector with lensesquite closed. Light was seen up to 180°. There was no definitemargin at any point, for disappearance was gradual. Then camethe question of how much of this light belongs to aperture inrelation to diameter of front lens and focal distance. The diameter of front lens to edge, as measured by micrometer,was 043 of an inch. If anyone had a
Monthly microscopical journal: transactions of the Royal Microscopical Society, and record of histological research at home and abroad . ject-glass of 120°. Is all aperture beyond 120° then useless ?I next measured the Tolles ^th in the ordinary sector with lensesquite closed. Light was seen up to 180°. There was no definitemargin at any point, for disappearance was gradual. Then camethe question of how much of this light belongs to aperture inrelation to diameter of front lens and focal distance. The diameter of front lens to edge, as measured by micrometer,was 043 of an inch. If anyone had asked me what diameterwould be required for 180° ? not wishing to exaggerate (as somemight argue that even space must have its limit), I should havesaid not less than the crown of your hat. Therefore a diameterof 04:3 for an angle of 180° is a marvellous accomplishment. If1 had also been asked what focal distance could be got with 180°?my answer would have been • 000, but the actual distance in thislens was OlS, a most comforting length for 180°. * M. M. J.; March, 1873, p. 124. 114 Angular Aperture of Object-glasses. Mr. ToUes has admitted that his judgment is not warped by anytheory, I must, however, trouble him with a Httie—a very Httle — not more abstruse thanthat the combination of twoquantities produce a third,or that three points make atriangle. Let us take, then,a diameter line of 43, anda median height of 13, andwe have here om- angle,Fig. 1, 118^, all that the object-glass can take in by carefully-ascertained dimensions. Thus, in this case, from the fact of plainmeasurement, an aperture beyond 118° is impossible. Were it merely my purpose to point out errors, I might nowstop; but there is no benefit to the community at large unless therelations of cause and effect are investigated. The appearance of ex-cessive aperture has always been- a vexed question with me, havingseen numerous instances where extreme rays form no image. Onlooking obliquely with
Size: 2584px × 967px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, bookpubli, booksubjectmicroscopy
