ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



671 



Fig. 117. 



fine adjustment screw. By tightening the clamping screw, the 

 adjustment is in order for the work of the combination ; by loosening, 

 for that of the coarser screw 

 only. As the thread of this 

 is a very little coarser than 

 the ordinary micrometer- 

 screw, it alone gives a better 

 motion for medium powers 

 than the fine adjustment in 

 common use, a second advan- 

 tage of the invention. The 

 combination of screws in use 

 on these Microscopes gives 

 a motion equivalent to that 

 of a screw having three hun- 

 dred and sixty threads to the 

 inch. Any desired combina- 

 tion can be made." 



The stage consists of a 

 strong, polished glass plate, 

 made secure by a brass frame, 

 which is nickel-plated. The 

 glass plate has a hole in the 

 centre, and is ground to 

 permit the greatest obliquity 

 of light. A new object- 

 carrier, consisting of an orna- 

 mented brass frame, with a 

 rest for the object - slide, 

 removable clips, and two 

 handles, moves with evenness 

 upon the stage, to which it 

 is pressed by lever springs, 

 with double joint, to permit 

 motion in every direction, 



and from which it is kept by frictionless pins that do not scratch the 

 stage. The whole carrier can be removed and its place supplied with 

 spring clips. 



The substage slides along the mirror-bar, thus keeping the 

 diaphragm or other accessory concentrically with the mirror upon the 

 object with central as well as oblique illumination. It can be removed 

 without interfering with the mirror. 



The diaphragm is of novel construction, and is fitted to the sub- 

 stage. It is of such form that it can be brought close to the slide, 

 and its openings brought in use without changing its position on the 

 mirror-bar. 



The mirror-bar swings to an angle of 45° above the plane of the 

 object, allowing the mirror to be used as a condenser on opaque objects. 

 The mirrors have their centre of motion around the point where the 

 optical axis intersects the plane of the object. 



2 z 2 



