CARE OF THE MICROSCOPE 183 



sion oil of the high objectives are seen; and partial loss of 

 the water immersing the condenser is also visible. 



Care of the Binocular or Binocular Attachment. — This 

 must be used only with the tube length correct to a milli- 

 meter. Since the tube length is (or should be) invariable, 

 water-immersion objectives with correction collars are 

 especially suitable for use with a binocular. If the eye- 

 pieces are not often changed, less dust will get on the 

 prisms. The binocular attachment may be kept on the 

 microscope under a tall bell jar, a wooden ring being used 

 if necessary to supplement the height. The drawing 

 camera may be fixed to the right-hand tube, and the left 

 eyepiece covered with a disc of waxed paper or of ground 

 glass. When using the binocular attachment, it is of 

 advantage to have a microscope which will not incline 

 more than 45 degrees from the vertical. (The writer 

 has but once used his microscope horizontal in over 30 

 years.) It is also conducive to steadiness to have the 

 microscope screwed, or otherwise fastened down, to a 

 board, or to the table. 



Care of the Photographic Attachment. — Siedentopf's 

 "Phoku" apparatus is referred to here, as being, so far as 

 the writer knows, the first accurate camera of this kind. 

 Care must be taken that the tube length is correct to a 

 millimeter. The two homal projection lenses should be 

 treated with as much care as objectives. All ordinary 

 exposures can be made with the lever arm, the wire release 

 being only for short exposures, and being somewhat 

 liable to get out of order. With correct illumination, the 

 circular diaphragm below the plate is unnecessary. The 

 upper surface of the main prism must occasionally be freed 

 from dust and particles. When used with the microscope 

 inclined, as is best, care must be taken that its weight does 

 not make the body of the instrument sag backward and 

 finally topple over. 



Care of the Binocular Magnifier. — This is sometimes 

 made with four separate Porro prisms, as in field glasses, 

 but usually with two compact sets. Probably these 



