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XI. — On an Improved Method of making Microscopical Measure - 
ments with the Camera Lucida. 
By Sir Walter Sendall, K.C.M.Gr., M.A., F.R.M.S. 
(Bead 21 st October, 1891.) 
In fig. 77, a b c is a section, through the plane of the paper, of the 
draw -tube of the Microscope, in a horizontal position ; A is the 
extremity of the axis of the tube, from which the line A B is drawn 
perpendicular to the axis, and meeting the plane of the table in the 
point B. If A B, the height of the Microscope from the table, be 
Fig. 77. 
equal to ten inches, and a camera be placed at A, we shall have 
the arrangement commonly recommended for making drawings and 
measurements of the virtual image of an object, projected upon the 
plane surface of the table. 
With centre A, and radius A B, describe C B D ; take any points 
E, F, in the line E B F, and join A E, A F. Then, since the 
amount of magnification of the object, afforded by its virtual image, 
is dependent, at every point, upon the distance of the image from the 
eye placed at A, an inspection of the figure will show that it is only 
at the point B that we obtain a degree of magnification due to a 
distance of ten inches. At every other point in the surface of the 
