1896.J MICROSCOPICAL JOURNAL. 20*7 



spaces on eacli side of the illuminated field ; if too far 

 away, the centre of the field only will be bright. If the 

 light is a point or small disc the properly illuminated 

 field will appear perfectly round; with the elongated oil 

 or acetylene flame it will appear oval. The light once 

 properly placed should be fixed for future work. 



With the light fixed and position of microscope deter- 

 mined, the operation of photographing is comparatively 

 simple. When the observer finds a field which he desires 

 to photograph, the microscope is carried from the work- 

 ing-table to that of the apparatus, placed in the marked 

 position, and the light lighted. The operator then seats 

 himself at the microscope, attaches the proper objective 

 and substage attachments, focuses the former on the ob- 

 ject and the latter on the wire screen placed against the 

 lantern condenser, removes the screen, substitutes the 

 opal glass, and, if using an Abbe condenser, opens or 

 closes the condenser until the sharpest visual definition 

 of the object is obtained. The opal glass is then removed 

 and if required a light filter is placed between the lantern 

 and microscope. The working eyepiece is then removed, 

 a projection eyepiece inserted or an amplifier placed in 

 the draw tube, or, if it is desired to use the objective 

 alone, a tube of black paper, to prevent reflection, is 

 placed in the tube of the microscope. The camera is then 

 attached to the microscope and the projected image 

 focused on the camera screen, preparatory to exposure. 



In regard to the method of projection of the image 

 much has been written regarding the relative value of 

 using the objective alone, or with an amplifier in the draw 

 tube, or with the ordinary working eyepieces or projec- 

 tion eyepieces of Zeiss. Practically, for all except the 

 highest-power diatom method, equally good results can 

 be obtained by either method, though where much work 

 is to be done there are some advantages in the use of the 

 projection eyepieces. 



