810 NOTE ON LKTTZ NEW MTCRO^irOPE STAND. 



The microscope is fitted with a substage taking an Abbe 

 chromatic condenser of the two lens type ; this part of the sub- 

 stage is fitted with rectangular centring screws, the two 

 screws pushing a ring against a spring. Beneath this there is 

 an iris diaphragm, having 13 leaves, and of first-rate manufac- 

 ture; in fact, the smoothest working iris I ever handled. This 

 iris is not attached to the same fitting as the condenser, and 

 therefore it is not controlled by the centring screws. It turns 

 out on an arm, and is fitted with Abbe's rack work eccentric 

 gear, which is perfectly useless, and much in the way. It would 

 have been better if the iris had been attached to the bottom of 

 the centring ring ; it would then have been centred together 

 with the optical part. 



This condenser fitting is drawn out into a kind of tail piece, 

 to which the mirror is attached ! It follows, therefore, that 

 when you alter the focus of your condenser you move also the 

 mirror, and consequently alter your light ! With daylight this 

 would hardly be noticed, but with lamplight it must cause 

 serious inconvenience. 



We now come to an altogether novel procedure in microscope 

 construction. This is to be found in the substage rack work. 

 It is well-known that two methods are in vogue here, viz., a 

 right and a wrong way, the right method being that of sprung 

 grooves, and the wrong being a solid ploughed groove, the 

 tightening up being performed by forcing the pinion into the 

 rack. Here, we have an entirely new departure. Fig. 1, shows 

 the plan of the substage slide. Fig. 2, shows the elevation, and 

 Fig. 3 the elevation of the ploughed groove fixed to the micro- 

 scope stand. The first thing that strikes one is that the rack 

 is not in the groove, but at one side of it, Fig. 1, so also is the 

 pinion in the other part. Fig. 3. 



Secondly, there is no V-shaped groove at all, but instead of 

 this there is a flat piece of steel (see shaded portions of Figs. 

 1 and 2), which is pressed downwards by a spring, this is 

 tightened up by a screw, shown at the lower part of Fig. 2. 

 This, of course, engages in the slot of Fig. 3, the flat part of 

 the slide bearing on the small flat tops of the slanting portions 

 of Fig. 3. 



This seems to be a very simple and smooth form of slide for 

 microscope movements. It is quite new, and, therefore, it 



