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APPENDIX. 



jected image of an object with the scale which was made 

 under like conditions, without again making use of the 

 stage micrometer. 



Mode of drawing microscopic objects. The 

 most convenient and ready way of delineating an object 

 is to sketch it with the free hand on paper placed at the 

 right of the microscope, the left eye being applied to the 

 tube. But if perfect accuracy of size and relations of 

 parts are desired, the outlines are first traced with a 

 camera lucida. The simplest for ordinary use is that of 

 Zeiss (Fig. 35), which is a combination of two prisms so 



Fig. 35. 



Camera lucida, for tracing the outlines of an object without tilting or 

 otherwise disturbing the microscope. 



The metal ring fits on to the upper end of the microscope tube, and the aperture, 

 a, is placed immediately over the eye-glass, this part of the camera being 

 somewhat more depressed than is represented in the figure. 



arranged that when placed above the ocular the surface 

 of the table in front of the microscope is seen at the same 

 time as the object, the image of the one being superposed 

 on that of the other. The paper for drawing is placed on 

 this part of the table, supported upon an inclined plane 

 of wood, and the main outlines are traced out on it, the 

 details and shading being afterwards filled up without 

 the camera. 



The lines of the stage micrometer can very easily be 

 traced in the same way by aid of the camera lucida. 



