Journal - Franklin Institute of the State of Pennsylvania (1826)
Franklin Institute, Philadelphia, Franklin Institute (Philadelphia, Pa.) · [Philadelphia : Franklin Institute] · leaf 197
an angle of 45°; o o, two of thethree springs carrying the plane mirror; these are seen edgewise fromeither end of the main tube ; e the draw-tube, to which the variouseye-pieces are fitted; ^ the focussing screw; andr^ the focal point ofthe converging cone of rays from speculum, which impinge on… … In Fig. 4 the illuminating apparatus is shown separately. A is a.slip of red glass (other colors can be used at pleasure), which can readilybe withdrawn or inserted by the fingers at J.^; B,a. circle of opal glass,held by thick india-rubber washers J, I, on each side; this is to miti-gate the…
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