432 KU.MMAUY OF CUERENT llESEARCHES RELATING 10 



the cover-glass holder can be placed and revolved freely. It obviates 

 the continual removal of one piece of apparatus with its objective, and 

 the screwing in of another in its place, and apparatus of this description 

 should simplify working, and is to be commended. 



The " Speera " binocular magnifiers should be of interest to most 

 microscopists on account of the many occasions when a low magnifying 

 power is required. The lenses are mounted at slightly convergent 

 angles, so that one image only is seen at the focal point. The lenses 

 are achromatic and give a stereoscopic effect. The focal lengths of the 

 pairs of lenses are made 5 in., 7 in. and 10 in., giving magnifications of 

 about 3*5, 2*5 and 1*75 diameters respectively. The great advantage 

 lies in the freedom which is given to both hands for dissecting or 

 working when these spectacles are worn. 



In " Critical Microscopy," by A. C. Coles, an illustration is given of 

 that writer's arrangement of instrument, lamp and accessories, which is 

 always available for reference in its working position. This has been 

 reproduced for commercial purposes as the " Physician's Outfit," and 

 is shown in tig. 4. To the busy worker an arrangement of this 

 description will readily appeal. If interrupted, it is only necessary to 

 cover the microscope with the glass shade and extinguish the lamp ; 

 everything is then left ready for continuing investigations when time 

 allows. 



B. Technique. 



Adjustable Dark Ground Immersion Illuminator. — The outstand- 

 ing characteristic common to all high power dark ground illuminators is 

 that if they are not accurately focused the object to be examined is not 

 illuminated at all. The light passes through a point and does not enter 

 the microscope unless the object is at that position to reflect this light. 



This peculiarity necessitates the use of selected slips of the exact 

 thickness suitable to the focus of the illuminator. Apart from the 

 trouble involved in selecting the slips, this does not present any special 

 difficulty where living specimens are being studied in leisurely fashion, 

 but in a laboratory liable to " rush " periods, it frequently happens that 

 the additional information afforded by dark ground illumination is lost 

 owing to the specimens having been mounted upon an unselected slide 

 of unsuitable thickness ; and, moreover, this form of illumination can 

 seldom be used for mounted specimens. We therefore welcome the 

 novel high power dark ground illuminatory introduced by Messrs. R. & 

 J. Beck, which is so made that, by moving the lower lens while the 

 upper lens remains in immersion contact with the slip, any focus of 

 from h mm. to 1^, mm. can be obtained -a variation of sufficient range 

 to accommodate any ordinary slip ; moreover the focusing adjustment 

 will be found valuable even with slips of selected thickness, as a slight 

 variation of the focus gives somewhat different effects. 



The method of adjustment is readily followed from reference to 

 fig. 6. AVhen the movable lens of the illuminator is raised or lowered 

 by means of the projecting lever handle (c), a ring outside the mount 

 also moves up and down, thus making a gap (b) that appears in the 

 upper part of the mount larger or smaller. The slide on which the 



