PHOTOMICROGRAPHIC APPARATUS 



up the apparatus for photomicrography : the Horizontal, 

 in which the optical axis is parallel with the table, 

 and the Vertical, in which the camera is supported 

 above the microscope. Preference is generally given to the 

 former, particularly if a rather complicated illuminating 

 system is employed. But many workers prefer the vertical 

 arrangement, which has the great advantage that, with a 

 simple lamp and condenser , an optical bench is unnecessary, 

 as correct adjustment of the illumination can be carried out 

 by means of the mirror. It is also more portable and com- 

 pact, and with preparations in liquids it is generally the 

 only practicable method to use. Each method has its 

 advantages, and if a camera has to be adapted the choice 

 may depend on its greater suitability for one or the other 

 system. 



No doubt the most universally serviceable stands are 

 those made for both horizontal and vertical work, but 

 caution must be exercised to make sure that no loss of 

 stability is involved in the arrangement, and every possi- 

 bility of vibration of the camera should be avoided. 



A photomicrograph may be taken after no further 

 preparation than is involved in placing the camera, 

 microscope, and lamp in a straight line on a table, 

 but the difficulties that have to be faced when 

 using such an apparatus for anything but the lowest 

 powers are at once apparent. Movement of the 

 camera is almost inseparable from the action of draw- 

 ing the slide, and renders accurate focussing of no 

 avail. The readiest way to prevent this disturbance is to 

 clamp the camera to the table ; but other difficulties 

 connected with the proper centration of the various 

 lenses are also encountered, and as a rule it takes much 

 longer to get the apparatus properly together and the 

 illumination adjusted than to take the photograph and 

 develop it. When changes of magnification involving 

 alteration of camera extension have to be made, there 



