THE MICROSCOPE. 



23 



Microscope, and ministers to its slightest defects. 

 A little instrument called an erector ', composed of 

 a lens which reverses the picture once more, is 

 supplied by the optician, and can be had by 

 those who practise the refinements of microscopic 

 observation. 



It is a good plan to make drawings of all objects 

 examined, or at any rate those which are new to 

 the observer. A note-book should be kept for this 

 purpose, and what cannot at once be identified by 

 the object, may afterwards be so by the drawing. 

 All persons, however, have not the gift of drawing, 

 and for those who need assistance in this way, the 

 camera lucida has been invented. This instrument 

 is applied to the tube of the Microscope when placed 

 at right angles with 

 the stem, in such a 

 way that a person 

 looking into it sees 

 the object directly 

 under his eye, so that 

 he may easily draw 

 its form on a piece 

 of paper placed un- 

 derneath. (Fig. 11.) 

 Some little practice 

 is, however, necessary 

 before the observer 

 can obtain satisfac- 

 tory results with this 

 instrument. It is 

 absolutely essential 

 that the eye should 

 be so placed that, 

 while one part of the Fig. 11. Camera Lnci^a. 

 pupil receives the rays from the reflecting surface 

 of the prism, the other sees the paper below with 



