ioo NATURALISTS' ASSISTANT. 



from the paper beneath passes through the prism and enters 

 the eye in the same direction as the first. These lines of 

 light are represented by dotted lines in the figures. It will 

 thus be seen that the eye perceives the object under the 

 microscope and a paper placed beneath, superimposed upon 

 one another. Its method of use is as follows : the micro- 

 scope is first focussed upon an object and then the tube is 

 brought to a horizontal position, the camera attached to the 

 eye-piece and a paper placed on the table beneath the camera. 

 Then looking down through the camera, one perceives at the 

 same time the paper and the object. A pencil may now be 

 made to trace on the paper the outlines of the object, and 

 the details afterward filled in free hand. 



In the first figured camera the image by the two reflections 

 is first reversed and then reversed again, bringing it the same 

 as that seen by direct observation through the tube, giving 

 an outline, the details of which are easily filled in. 



The second form having but a single reflection produces a 

 reversed image, and hence it is difficult to complete free 

 hand. Instead of a prism, the student may easily make his 

 own camera of this second form by mounting a piece of thin 

 glass in a bit of cork which can be affixed to the tube of the 

 microscope. 



A third form, which is rarely seen in America, but which is 

 in the opinion of the writer the best, is the "vertical" camera, 

 manufactured by Carl Zeiss. This form may be applied to 

 the microscope when in a vertical position, throwing the im- 

 age to one side of the stand, and giving the clearest image 

 of any, of both object and pencil. It is also remarkably cheap 



