66 ELEMENTARY PHOTO-MICROGRAPHY. 



This fact is often demonstrated by placing one 

 of these compound eyes, mounted flat on a glass 

 slip, on the stage of the microscope, when any 

 well-defined object may be seen repeated in each 

 of the facets. As a matter of curiosity this is most 

 interesting, and it affords excellent practice in the 

 art of focussing. The picture of the object to be 

 repeated should be first made on a lantern slide 

 in the usual way, and masked to show only the 

 part to be photographed. This should be small 

 enough to show as a transparency within an open- 

 ing of Jin. square, the rest of the slide being blocked 

 out. With the microscope in its horizontal position, 

 place this transparency vertically about midway 

 betwixt the lamp and substage condenser, and at 

 the right height to correspond with axis of micro- 

 scope and the prepared eye (which can be pur- 

 chased for i /6) on the stage. The iin., Jin., or Jin. 

 objective can be used either with or without eye- 

 piece. First try with Jin. objective and " A " eye- 

 piece, and focus on the mounted eye. It is at this 

 point where difficulty occurs, but it must be re- 

 membered that what has to be found is the aerial 

 image of the object as it is focussed by the lenses 

 of the compound eye, which will be at a point 

 nearer to the observer than the plane of the eye on 

 the glass slip. If, therefore, the objective be very 

 slowly racked out of focus, a point will be reached 

 when an image will be seen in every facet of 

 the eye. 



