THE CAMERA LUCIDA. 



101 



THE CAMERA LUCIDA. 



The Camera Lucida, fig. 68, was invented by Dr. WoUaston, in 

 1807 : it is a valuable addition to the microscope, for making drawings 

 of structures, and for obtaining, with a micrometer, accurate measure- 

 ments. It consists of a four-sided prism of glass, set in a brass frame 

 or case, as represented in the figure annexed ; and by means of a short 

 tube it is slipped over the front part of either of the eye-pieces, its cap 

 having been previously removed. Mr. Ross attaches the prism, by 

 two short supports, to a circular 

 piece of brass at the end of the 

 tube ; on this it can be slightly 

 rotated, whilst the prism itself can 

 also be turned up or down, by 

 means of two screws with milled 

 heads. So arranged, the camera 

 may be adapted to the eye-piece, 

 the microscope having been pre- 

 viously placed in a horizontal po- 

 sition ; if the light be then re- 

 flected up through the compound 

 body, an eye placed over the 

 square hole in the frame of the 

 prism will see the image of any 

 object on the stage upon a sheet 

 of white paper placed on the table 

 immediately below it. But should 

 it happen that the whole of the 

 field of view is not well illumi- 

 nated, then, either by revolving 

 the circular plate or turning the 

 prism upon the screws, the de- 

 sired object will be efifected. The chief ■difficulty, in the use -ctf this 

 instrument is for the artist to be able to see, at one and the same 

 time, the pencil and the image. To facilitate this in some measure, 

 the one or two lenses below the prism wUl cause the rays from 

 the paper and pencil to diverge at the same angle as those received 

 from the prism, whereby both object and pencil may be seen with the 

 game degree of distinctness. 



i^ofessor Quekett gives the following directions for using the Camera 



Bg. 68. 



