54 THE USE OF THE MICROSCOPE 



suggested that a sliding sleove to oach eyepiece, with an exten- 

 sion movement of about 25 iniUimeters, and a retraction of 5 

 milHmeters, might suffice. 



5. The single tube should be interchangeable with the double 

 tube, being occasionally required for short duration vision, and 

 always for photography. 



6. The Siedentopf binocular attachment is equal to the 

 binocular without an amplifying lens. 



7. When using the monobjective binocular with parallel 

 tubes, the presence of any strong stereoscopic effect shows that 

 the distance between the eyepieces, or the centering of the eyes, 

 is wrong. 



8. The camera lucida can be used on the monobjective binocu- 

 lar with parallel tubes by covering one eyepiece with a disc of 

 ground glass. 



9. There should be a screen fitted in front of the eyepieces of 

 the binocular microscope to shade the eyes from front light. 



10. With parallel tubes, distance spectacles, noi reading glasses, 

 should be used. For reading glasses have their centers 5 

 millimeters or so too near, and so cause eye strain and poor 

 vision. 



11. With the monobjective binocular with converging tubes, 

 reading spectacles, not distance glasses, should be used. For 

 the distance glasses have their centers about 5 millimeters 

 farther apart than the converging eyes need for accurate 

 centering. 



