52 THEMICROSCOPIST. 



3. The best position for microscopic observations is when 

 the observer is lying horizontally on his back. This arises 

 from the perfect stability of the head, and from the equality 

 of the lubricating film of fluid which covers the cornea. The 

 worst of all positions is that in which we look downwards ver- 

 tically. The most common and easy position is generally with 

 the instrument inclined at an angle of 45 degrees. 



4. If we stand straight up and look horizontally, parallel 

 markings or lines will be seen most perfectly when their direc- 

 tion is vertical; viz., the direction in which the lubricating 

 fluid descends over the cornea. 



5. Every part of the object should be excluded, except that 

 which is under immediate observation. 



6. The light which illuminates the object should have a 

 very small diameter. In the day-time it should be a single 

 hole in the window shutter of a darkened room, and at night 

 an aperture placed before an Argand lamp. 



7. In all cases, particularly when high powers are used, the 

 natural diameter of the illuminating light should be diminished, 

 and its intensity increased, by optical contrivances. 



The following remarks by Mr. James Smith, copied from 

 the Microscopic Journal, vol. i., are recommended to the con- 

 sideration of all who are in the habit of using microscopes. 

 "Much of the beauty of the objects seen depends upon the 

 management of the light that is thrown upon or behind them ; 

 which can only be fully mastered by practice. It may be 

 remarked, however, as a general rule, that in viewing those 

 which are transparent, the plane mirror is most suitable for 

 bright daylight ; the concave for a lamp or candle, which 

 should have the bull's-eye lens, when that is used, so close to 

 it that the rays may fall nearly parallel on the mirror. If the 

 bull's-eye lens is not used, the illuminating body should not 

 be more than five or six inches from the mirror. The latter 



