164 APPENDIX. 



BINOCULAR PHOTOGRAPHY. Stereoscopic photo- 

 graphs may be produced by Stephenson's Binocular 

 arrangement, Polycystinas and Discoid al Diatoms 

 form beautiful objects when seen in the Stereoscope. 



The prisms should be placed as near the back of 

 the objective as possible, and an ordinary stereos- 

 copic camera substituted for that already mentioned. 



Wenham's and most other arrangements are com- 

 paratively useless, as the illumination is unequal on 

 the plates, and they require to be placed at an in- 

 convenient angle. 



FOCUSSING AT A DISTANCE. The ordinary rod and 

 cork already described will be improved by the fol- 

 lowing addition. The cork being made slightly 

 smaller than the fine adjustment, three pieces of split 

 cane almost large enough to surround it, and long 

 enough to project a few inches beyond the end 

 farthest from the rod, are glued and tightly fastened 

 to it. A wire ring made to slip up and down on 

 these canes, forms a large crayon holder which will 

 grasp any sized adjustment firmly. 



