80 PRACTICAL PHOTO-MICROGRAPHY. 



to hold a few inches behind its late position a piece of white 

 paper or cardboard. On this white surface the image is visibly 

 projected, and uneven lighting easily detected. 



In most cases the ground glass of the camera and the 

 coarse adjustment of the microscope permit of sufficiently 

 accurate focusing with very low powers, but a " Eamsden " 

 eye-piece placed on the plain glass focus-screen may be found 

 preferable in conjunction with the fine adjustment of the 

 microscope. Often, however, where a good general appearance 

 is wanted the unaided eye and ground glass are better in 

 practice. 



Our ground-glass disc illuminated by parallelized rays, as 

 figured No. 26 on page Yl will be found most convenient for 



O i o 



this class of work. 



While the object is being examined in the microscope with 

 the ocular, the part of the object occupying the centre of the 

 field should be carefully noted ; this point must occupy pre- 

 cisely the centre of the ground-glass where the camera is 

 attached. If the apparatus is of the construction suggested on 

 page 51, where the microscope and the light are fixed in their 

 relationship to each other, and where the table bearing them 

 rotates to a " stop " when the camera is about to be attached, 

 it is important to note at the very first whether the centre of 

 the object coincides precisely with the centre of the ground- 

 glass when the image is seen on the ground-glass. The centre 

 of the latter should be marked in pencil on the ground side of 

 the glass ; this may be done by drawing diagonals and describ- 

 ing a little circle round the intersection of the diagonals. The 

 cardboard or other discs recommended on page 77, should have 

 apertures corresponding in size to the sizes of plates to be used. 



These remarks if carefully noted and acted upon will save 

 trouble in future, and the image being focused on the ground- 

 glass, the dark slide carrying the sensitive plate is inserted in 

 its place, the light shut off, preferably by a shutter working 

 very easily inside the camera, and all is ready for exposure, 

 remarks on which are left for a later page. 



Example No. 2. A subject similar to No. 1, but more finely 

 marked and smaller^ requiring more angular aperture, and stilJ 



