Monthly microscopical journal: transactions of the Royal Microscopical Society, and record of histological research at home and abroad . se divided into degrees. The body was sethorizontally, and a lamp placed some two feet away. The indexwas set with a half-luminous field, and the object-glass focussedcarefully on to the glass surface. Unless this is done there will beconsiderable error in the measurement. The microscope is nextrotated, and when the light again bisects the field, the degrees areread off. By these means the balsam aperture ivith closed lenseswas only 68, instead of 98° as stat

- Image ID: 2AJ92HJ
Monthly microscopical journal: transactions of the Royal Microscopical Society, and record of histological research at home and abroad . se divided into degrees. The body was sethorizontally, and a lamp placed some two feet away. The indexwas set with a half-luminous field, and the object-glass focussedcarefully on to the glass surface. Unless this is done there will beconsiderable error in the measurement. The microscope is nextrotated, and when the light again bisects the field, the degrees areread off. By these means the balsam aperture ivith closed lenseswas only 68, instead of 98° as stat
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Image ID: 2AJ92HJ
Monthly microscopical journal: transactions of the Royal Microscopical Society, and record of histological research at home and abroad . se divided into degrees. The body was sethorizontally, and a lamp placed some two feet away. The indexwas set with a half-luminous field, and the object-glass focussedcarefully on to the glass surface. Unless this is done there will beconsiderable error in the measurement. The microscope is nextrotated, and when the light again bisects the field, the degrees areread off. By these means the balsam aperture ivith closed lenseswas only 68, instead of 98° as stated; and this angle of 68° wasthe same whether water was introduced or not between the planesurface of front lens and semi-cylinder, taking care to focus in eithercase. The principle of operation was identical with that of theordinary sector, to the moving index aim of which the hemispheremay be supposed to be fixed, and the focal front of object-glass a, Angular AjJerture of Object-glasses. 117 Fig. 4, brought iu to the centre, &, of the semi-cyHnder c, at whichthere is a thin metal slit or stop of suitable diameter. Fto. 4.. In this measurement I have rather over than under estimatedthe aperture from using a stop too large; less than sVth of an inchwould have been more proper. Believing that apertures, to be correctly measured in future,must have all extraneous lateral rays cut off by a slit or stop of verythin foil in the focus of the object-glass, and as this requires to be anadjustable piece of apparatus, the following plan has been arranged. In order to prevent injury to the edges of the slit, and to keepthem in one plane, the two strips of foil (which may be of platinum)are cut with a knife along a steel straight-edge. One of these piecesis cemented on to a glass slip, the other is stretched across a per-forated metal plate shding on the top of the glass, and adjustable bya screw. The edges of the two strips abut against each other, andare adjusted for parallelism by se

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