251 



cient degree of steadiness for common purposes. But by sliding 

 a couxmon Jlat-iron into its interior it becomes as firm as the most 

 ponderous instruments of Ross, which are too heavy to be carried 

 about with comfort. 



2. The facility with which the heujht of the compound body, 

 as w-ell as its inclination, may be varied by means of the " slots " 

 and notches in the bearing semicircle. 



3. The mode of focal adjustment by rotation of the tube, or 

 compound body. This has a movable ring upon it with a pro- 

 jecting spur, which bears against the slightly inclined posterior 

 surface of the anterior V-shaped support of the tube. The disk 

 which protects the eyes is used as a levei", and thus a very smooth 

 and uniform motion without the smallest amount of " lost time " or 

 " back lash " is obtained without rack and pinion, spring or screw. 



4. The open horseshoe stage, with the movable object-holder 

 received upon its remote (anterior or inferior) surface, the glass 

 object-slide being itself pressed by springs against the remote 

 surface of the object-holder. It follows from this arrangement, 

 1st. That if one object is in focus, all others mounted in a similar 

 manner are in focus, or very nearly so ; 2d. That the thickness 

 of the stage becomes practically reduced to nothing, as the glass 

 slide is next the lamp, and behind, or below, every thing except 

 the springs that press it forward against the remote face of the 

 object-holdei". 



5. The double radial stage-movement. The horseshoe piece 

 next the observer turns from side to side on a screw passing 

 through the lower or middle portion of its arc. The other horse- 

 shoe piece turns on a screw fixing it to one arm of the first, so 

 that it moves up and down. The arcs they follow form so small 

 a part of a circle that the eye cannot distinguish their movement 

 from a rectilinear one. The holt and crossbow flat handles, 

 working singly or together, make the management of the stage 

 movement very convenient. 



6. The flat-wicked lamp, so mounted as to move freely without 

 the possibility of slipping, at whatever angle the apparatus may 

 be inclined. 



7. The combination of mirror and lens in an open frame, so 

 as, by slight alterations, to serve a triple purpose ; that of plane 

 mirror, of a condenser, and of a substitute for the concave mirror. 



