ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 455 



Horizontal Position of the Microscope. * — Mr. H. J. Slack con- 

 siders that the usual position of a Microscope with a tube slanting a 

 little and the head leaning forward to look down it, is all very well 

 for a short examination of any object, but not at all desirable for 

 continuous work. A better plan is to get a carpenter to make a light 

 stool 2 ft. long and 14 in. wide, standing on four legs, the length of 

 which should be determined by that of the Microscope it is intended 

 to use and the height at which the observer sits. His own stool 

 is 7 in. high, and when placed on an ordinary table brings a full-sized 

 Microscope with its tube in a horizontal position at a convenient 

 height for the eye of an observer sitting in an ordinary chair. The 

 late Mr. Lobb, who was skilful in exhibiting troublesome objects, 

 always used his Microscope in this position ; but as far as Mr. Slack 

 knows, it is seldom adopted. When the instrument is in position as 

 described, the substage mirror should be turned out of the way, and 

 the lamp placed so that its flame is exactly opposite the axis of the 

 instrument, and can be seen in the middle of the field on looking 

 through it. If the objects to be watched are large enough for a low 

 power, the light may be softened by placing under the slide a piece of 

 foreign post paper saturated with spermaceti. For high powers, an 

 achromatic condenser is desirable, and one of the smallest central 

 stops is usually the most useful for displaying fine cilia, or delicate 

 whips, as well as for lighting up without glare the interior of various 

 creatures. If all is arranged properly, the manners and customs of 

 infusoria may be watched for hours without more fatigue than reading 

 a well-printed book. A tenth part of the time spent with the head 

 leaning forward in the usual way is far more exhausting. 



Flogel's Dark Box. — Dr. J. H. L. Flogel some fourteen years ago 

 devised the dark box, shown in fig. 65, to put over the Microscope 

 and shut out all extraneous light. It is open behind and has an aper- 

 ture in front to admit light to the mirror. From back to front it 

 measures 20-25 cm., and in width 60-80 cm. ; its height depends 

 upon the stand to be used.f He now adds a few words in the interest 

 of those microscopists who may wish to have similar boxes made. | 



The principal thing is the right position of the aperture by which 

 the light is admitted ; its upper edge must lie exactly at the level 

 of the stage — not lower, in order that the full light from the window 

 may be used ; and not higher, in order that light may not fall from 

 above on the stage, which would do away with most of the advantages 

 of the box. The Microscope is put as far as possible in the box, so 

 that the edge of the stage touches it, and, in order that there may be 

 sufficient room for the head of the observer in this position, the 

 anterior portion of the box is bowed out. On the right and left of the 



* ' Knowledge,' v. (1884) pp. 109-10. 



t Dr. L. Dippel considers this plan preferable to a darkened room with an 

 opening in the shutter to admit light. The contrast between the illuminated 

 field and the dark room is too great. The pupil of the eye is now enlarging and 

 now contracting, and injurious results must inevitably follow. ' Das Mikroskop,' 

 1882, pp. 751-2 (1 fig.). 



X Zool. Anzeig., vi. (1883) pp. 566-7. 



