148 ANNUAL OF SCIENTIFIC DISCOVERY. 



" As I do not iiitt'iid here doscrihinj^ the instninuMit in detivil, I 

 will only say that it consists es.<;i'ntially of a rcctanj^iihir brass box, 

 havings the 'society screw' at the top, to attach it to any micro- 

 scope tnbc, and at the bottom, to rc'ccive any objective ; and so 

 constrncted that it can l)e placed in any position with regard to the 

 li;rht. A brass draw, moved by screw and milled head, slides into 

 the box, and carries a relleetor of silv«u", also movable on its own 

 axis by means of small milled heads: the forward edp^e of the 

 reflector is cnrved, and it is concave, havini^ a focns of about six 

 inches. By means of the screw, the ourvccl edge of this i-eUector 

 can, when adjusted at an an<^le near forty-live degrees, be pushed 

 more or less over the opening at the back of the objective. Oppo- 

 site to the relleetor, and attaehe(l to one side of the box, is a re- 

 volving circle of iliaphragms, of great use in regulating the; light, 

 so as to exclude all fog or glare; the ajiertures vary from three- 

 twentieths to one-twentieth (jf an inch. 



" As the ' illuminator' is already in the hands of many, I append 

 a few simple directions as to its use. The objective must be 

 adjusted for an uncovered object, though 1 find few are rightly 

 marked. An ordinary i)aper-covered slide, witii bits of gold l(>af 

 on it, answers athnirabiy as an ol)ject to adjust the light. The 

 illuminator being screwed on to the tube, and the circle of dia- 

 l)lnagms jdaccd facing the light (1 find the ordinary coal-oil lamp 

 Avith fiat fiame to answer admirably, the fiat side being toward the 

 refieetor), turn the icllector at an angle of al)ont forty-five degrees, 

 and allow the liglit to enter the largest aperture of the diaphragm. 

 By means of the screw, push the reflector forward nearly as far as 

 it will go. Turn the; reflector on the axis of the tube and on its own 

 axis, mitil the liglit, which may be placed ten or twelve inches to 

 the left of the microscope, and directly opposite the circle of dia- 

 phragms, is reflected down on the paper-covered slide, the tul)e 

 of the microscope i>eing racked up to about the position it will 

 occujjy when the objective is screwtid on and in focus. The light 

 thus reflected down should appoar just at the curved edge of the 

 reflector, in the axis of the tube, when looking through the tube, 

 the eye-piece being removed. Now screw on the objective, and, 

 before replacing the eye-piece, bring it into focus. The field will 

 appear brilliantly illuminated, as in using a lens with a Liebcrkuhn ; 

 if not, a slight movement of the reflector, or diaphragm, or light, 

 will quickly accomplish this. Put in the eye-piece and adjust for 

 focus; if the field is not clearly illuminated, say with one-fifth-incli 

 objective, a lijtle fingering of the reflector, or diaphragm, will 

 suffice to effect this. The screw which moves the draw and 

 reflector may now be withdrawn, uncovering all but about a quar- 

 ter or one-half of one side of the posterior lens of the objective ; 

 and, if care has been talcen to properly adjust the diapliragm and 

 reflector, a most brilliantly illuminated field, free from all fog and 

 glare, will reveal objects with a beauty and clearness inconceiv- 

 able by those who have never used high powers of the microscope 

 upon opaque oljjects. The most common objects appear with new 

 and hitherto unexpected beauty, brilliant not only with their own 

 proper colors, but reflecting iridescent tints from their membranes. 



