DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 129 



piece may be conveniently removed from the body of the 

 microscope, and the end covered with a cap, having a 

 plate of finely ground or greyed glass fitted into it. On 

 this plate the image of the object will be formed, and 

 distinct vision obtained by adjusting the focus in the 

 usual manner. In this case, the eye-end of the micro- 

 scope, in order to produce the desired effect, must be 

 kept darker than the other extremity. If, instead of the 

 plate of glass, a piece of tracing paper be employed, the 

 image may be delineated at once. Also, the glass may 

 have divisions marked upon it similar to those in the 

 plate, fig. 13, and be used with drawing paper traversed 

 with squares, on Mr. Bauer's plan, described in the 

 Micrographia. 



One great advantage which the camera lucida derives, 

 from its connexion with the telescope or microscope, is, 

 that the reflected image is thrown on the drawing paper, 

 so as to appear in the same plane with it. When it is 

 used without either of these instruments, the image 

 is formed at the same distance below it as the object is 

 distant from it in front ; thus occasioning an error by 

 parallax with the image and pencil, upon the slightest 

 motion of the eye. 



Beginners in drawing experience some difficulty in 

 obtaining a distinct view of the point of the pencil simul- 

 taneously with the magnified image. The Rev. J. B. 

 Reade informs me, that by illuminating the object with 

 strong lamp-light in the day-time, and the paper on 



