. Physical laboratory experiments : mechanics, optics and heat. acloud. These are reflected by a plane mirror in the directionof the axis of the instrument. After passing through thecondenser diaphragm, CD, the rays are collected by a con-densing lens and focussed on the object at Oi. They then passthrough the objective, the upper focal plane of which is atFi. By the interposition of a collecting lens in the path ofthe rays the real image, O2, of the object is transposed fromFi to O3 in the plane of the eye-piece diaphragm. Whenviewed through the eye-piece, this image is seen as a magnifiedvir
. Physical laboratory experiments : mechanics, optics and heat. acloud. These are reflected by a plane mirror in the directionof the axis of the instrument. After passing through thecondenser diaphragm, CD, the rays are collected by a con-densing lens and focussed on the object at Oi. They then passthrough the objective, the upper focal plane of which is atFi. By the interposition of a collecting lens in the path ofthe rays the real image, O2, of the object is transposed fromFi to O3 in the plane of the eye-piece diaphragm. Whenviewed through the eye-piece, this image is seen as a magnifiedvirtual image, O4, at a distance C= 10 inches, or 250 millimetersbelow the eye-point, EP, this being the distance of most distinctvision for the normal eye. The distance between Fi and F2is called the optical tube length; the distance, L, is the me-chanical tube length, » Figures 12 and 13 refer speci6cally to the Bausch and Iximb microscopes used in thisexperiment, and are reproduced through the courtesy of the Bausch and Lomb OpticalCompany. THE MICROSCOPE 39. Fisr. 18. 40 PHYSICAL LABORATORY EXPERIMENTS The various parts of a microscope, Figure 13^ are designatedas follows: £? = eye-piece. D = draw-tube, for varying the magnification of the graduations on the tube give the value in milli-meters of the mechanical tube length, L, when nose-pieces are not used with the ^A/ = revolving nose-piece for carrying several objectives,which may be revolved into place as = objective in = rack for coarse = pinion head for focussing instrument milled head for fine adjustment of focus and, if grad-uated, for measuring the thickness of = handle arm. >S = stage for carrying object under = substage for carrying diaphragm and = mirror for illuminating object from = = = inclination joint. Illumination of the Object.—To obtain the be
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