On Stereomicrography. By G. P. Girdwood. 15 



able to extend the work, apply this method to other objects, and pro- 

 duce pictures of microscopic objects in relief, and thus give to students 

 a more realistic idea of the objects before them. 



The method adopted in taking the pictures exhibited with this 

 paper was to place an ordinary photographic camera horizontally on 

 the table, raised so that the opening for the lens should be just 

 centred with axis of the Microscope tube; when the Microscope was 

 turned on its stand to the horizontal position, a thin sheet of vulcanised 

 india-rubber was secured over the hole for the lens in front of the 

 camera, a small hole was cut in the centre of the rubber-sheet, and 

 the Microscope tube without an eye-piece was thrust through the 

 small hole in the rubber, which fits tight round the tube and stops 

 all light entering ; a small diaphragm was placed in the end of the 

 tube to stop light reflected from the inside of the tube, and the object 

 was illuminated by a coal-oil lamp placed opposite the opening in the 

 stage and condensed by a bull's-eye focussed in the usual way. If 

 necessary a micrometer might be used on the stage to show magni- 

 fication. 



In the case of the crystals of uric acid shown, a 1-in. object-glass 

 was used, 30 seconds exposure with a small single coal-oil lamp, and 

 the picture was developed with Kodinal developer in the ordinary 

 manner. In the case of starch-granules of ginger grown and prepared 

 by the author himself, a £-in. object-glass was used with polariscope ; 

 exposure for each picture half an hour. 



Since perfecting the apparatus for this work, the author has had 

 brought to his notice the original article by Sir Charles AVheatstone, 

 ■ Contributions to the Physiology of Vision, Part the First, On some 

 remarkable and hitherto unobserved Phenomena of Binocular Vision,' 

 Philosophical Transactions, 1838, reprinted in 1879, wherein the 

 correctness of the ideas the author had in designing this stage are 

 completely borne out. 



When a picture is taken by a Microscope, the picture of the object 

 is reversed, and when this negative is printed it is reversed again, so 

 that the print corresponds to the object itself as seen in the Micro- 

 scope ; but in transparent objects, reversal of the prints in mounting 

 would give a stereoscopic view of the object as seen from the other 

 side, which in some cases may be desirable. 



