144 THE AMERICAN MONTHLY [April 



which are embodied in the instrument now shown in Fig. 1. 

 The base is a heavy, circular ring turned in the lathe, both in- 

 side and out. On the face of the periphery is cast a boss, hav. 

 ing a slanting top. The pillar which carries the stage and arm 

 has its end faced to a similar angle, so that when the pillar i'^ 

 vertical it stands at right angles to the base. A square-should- 

 ered screw passes through the ring-base, and is tapped into the 

 bottom of the pillar. Great care must be taken tiiat the line of 

 this screw is exactly square with the facets. A centre for drill- 

 ing the pillar to can be found on the stage-i)late ; Init for the 

 ring-base it will be advisable to fix it on a slo})ing piece of 

 wood, attached to the face-plate of the lathe at a suitable angle, 

 and drill the hole through while running, using a countersink, 

 or pin-drill, for the square head of the screw ; or it may be 

 worth while to turn a flat-end cylinder of boxwood, with a cen- 

 tral hole to fit, and serve as a guide for a twist-drill, this guide 

 to be clamped or cemented in place on the flat. This will insure 

 the hole being drilled upright therewith. 



The microscope is shown in Fig. 1 in the vertical postion ; 

 but if we turn the base round to the place shown by the dotted 

 line, the pillar inclines backwards to an angle of about 50°, 

 which is suitable for observation while the user is seated. The 

 base coming behind aftbrds a firm support against any over- 

 hang. This movement is easier to make, and less cumbrous, 

 than the usual cradle-joint. The pillar is drilled through its 

 axis down near to the base, and finished with arose or cylinder- 

 bit, so as to get a true and smooth hole. Into this it fitted a 

 round rod, carrying the arm at the top, so as to slide smoothly 

 without any shake. The back of this rod is cut into a rack, 

 raised and lowered as usual by a pinion with two milled heads. 

 In the top of the pillar is fixed the arm carrying the body 

 through the socket-guide. However well a coarse focussing ar- 

 rangement, consisting of a side-racked tube or body sliding in a 

 socket, may appear to act while highly-polished just as it leaves 

 the optician's hand, it will not continue to do so, for when it 

 becomes tarnished the extra friction causes a nasty cross-strain 

 damaging to rack and pinion. If the sliding-tube is moved by 

 an equal force across the centre, the strain is equalised. This 

 is effected in this microscope by the arm at the top of the 

 racked rod, which ends in a horseshoe form, embracing the two 



