140 THE MICROSCOPE. 



heads. So arranged, the camera may be adapted to the 

 eye-piece, the microscope having been previously placec? 

 in a horizontal position ; if the light be then reflected up 

 through the compound body, an eye placed over the 

 square hole in the frame of the prism will see the image o^ 

 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 

 illuminated, then, either by revolving the circular plate or 

 turning the prism upon the screws, the desired object will 

 be effected. The chief difficulty in the use of this instru- 

 ment 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 will 

 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 same degree 

 of distinctness. 



The following is the method for employing the Camera 

 Lucida with the microscope. The first step to be taken, 

 after the object about to be drawn has been properly 

 illuminated, adjusted, and brought into the centre of the 

 field of view, is to place the compound body of the micro- 

 scope in a horizontal position, and to fix it there. The 

 cap of the eye-piece having been removed, the camera is 

 to be slid on in its stead : if the prism is properly 

 adjusted, a circle of white light, with the object within it, 

 will be seen on a piece of white paper placed on the table 

 immediately under the camera, when the eye of the 

 observer is placed over the uncovered edge of the prism, 

 and its axis directed towards the paper on the table. 

 Should, however, the field of view be only in part illumi- 

 nated, the prism must either be turned round on the eye- 

 piece, or revolved on its axis, by the screws affixed to its 

 frame-work, until the entire field is illuminated. The 

 next step is to procure a hard, sharp-pointed pencil, which, 

 in order to be well seen, may be blackened with ink round 

 the point ; the observer is then to bring his eye so near 

 the edge of the prism that he may be able to see on the 

 paper, at one and the same time, the pencil-point and the 

 image of the object. When he has accomplished this, the 



