168 THE USE OF THE MICROSCOPE 



faint brown, have given the best results with the 16-milli- 

 meter apochromatic; a light-blue glass screen being used, 

 and a vertical camera. With high powers, the Siedentopf 

 (Phoku) attachment has given the sharpest images of iron- 

 acetocarmine preparations with the apochromatic water 

 immersion 70 (or the oil immersion 90 of 1.4 aperture), 

 and a condenser cone of 1.0 to 1.2. A yellow-green screen. 

 No. 56, was regularly used. The diaphragm on the source 

 of light kept waste light from the inside of the microscope 

 tube, which was not illuminated; nor was there need of the 

 circular diaphragm provided for putting under the sensi- 

 tive plate. This method also obviated the use of a wide 

 tube, and of a black velvet lining to the tube. 



Short Wave-length Photography. — The ideal of micro- 

 scopical photography is to show, with blue or violet light, 

 details invisible or poorly visible to ordinary observation 

 with yellow-green light. The aperture is thus increased 

 by about one-fifth. The microscopist is still far from this 

 ideal. Only an easy method of making many photographs 

 will allow of the necessary practice. Special objectives 

 would seem to be needed. Probably the method of photog- 

 raphy with ultra-violet light, giving an aperture of about 

 2.5, has not yet been sufficiently worked with many objects. 

 (The ultra-violet light, however, tends to disorganize 

 organic bodies in watery liquids.) The monobromide of 

 naphthahn immersion with blue-violet fight should give 

 an aperture of about 2.0 for photography. 



Practice in Photography. — To attain success in micro- 

 scopical photography, one should start with photography 

 at low magnifications, say, 2 or 3 times, with an ordinary 

 camera; then use a 16-milfimeter apochromatic and a 

 projection eyepiece (or homal), and, finaUy, an immersion 

 objective and an immersed condenser. (In the writer's 

 experience, pictures taken with a 16-milfimeter apochro- 

 matic and compensating eyepiece, by altering the focus of 

 the objective, are not critically sharp.) 



Type of Apparatus. — The writer subjoins an account 

 of the apparatus he uses for photographs of chromosomes 



