INTRODUCTION. 



XXVll 



Camera Lucida of Chevalier. This instrument (fig. 10) is made by Hartnack. Instead of 

 the eyepiece, the tube / is fixed in the tube of the microscope. The observer looks through 



the small prism, and sees the outline of the 

 section thrown on the table, or on a piece of 

 paper laid on the table, close to the microscope. 

 A shade is placed in front of this, and must be 

 so adjusted that too much light does not fall 

 on the paper. The contour is then mapped 

 out with a pencil. 



Fig. 10. CAMERA LUCIDA OF CHEVALIER. 

 a the Instrument ; l> a section, showing the prisms. 



Fig. it. CAMERA LUCIDA (Zeiss). 



The ring of brass fixes it to the tube of the Microscope, 



and the aperture a is placed over the Eyepiece. 



Other Cameras. Much simpler forms arc the camera lucida of Nachet, or the one 

 made by Zeiss (fig. 1 1). The ocular is left in its place, and the camera is fixed to the tube of 

 the microscope by the ring of brass. The aperture a is placed immediately over the centre of 

 the eyepiece. On looking through this aperture the surface of the table in front of the micro- 

 scope is seen at the same time as the object. The drawing-paper is placed on an inclined 

 plane on this part of the table, and the outline of the object is sketched, whilst the details are 

 afterwards filled in without the camera. 



Neutral tint reflector. This simply consists of a small cap, which fits on the end of the 

 microscope, and in it is placed a piece of glass, at an angle of 45. The microscope tube 

 must be horizontal. On looking through the glass the image of the object is seen on the 

 paper. The same precautions with regard to the modification of the light on the paper must 

 be taken as for Chevalier's camera. 



It is not even necessary to have a brass cap to fit on to the microscope ; an ordinary cover- 

 glass, fixed to the eyepiece, by means of modeller's wax, at an angle of 45, answers the purpose 

 admirably. 



METHODS OF STUDYING THE PROPERTIES OF 

 LIVING PROTOPLASM. 



THE MOIST CHAMBER. 



Moist chamber of v. RecklingJiansen. This is easily made by cutting off the lower end of 

 an ordinary glass cylinder, such as is used for a paraffine lamp. Through the lower part of the 

 cylinder the tube of the microscope is placed. The lower end of the cylinder is ground flat, 



