110 SUMMARY OF CURRENT RESEARCHES RELATING TO 



MICEOSCOPY, &c. 

 a. Instruments and Accessories. 



Bausch and Lomb Optical Company's "Professional" and "Inves- 

 tigator" Microscopes. — (1) Professional. The description of this instru- 

 ment was received too late to be inserted in its proper place in order 

 of date, under the head of "Swinging Substages." * It appears to have 

 been made in 1876 (Fig. 4, one-third actual size). It is provided 

 with a heavy brass foot, inlaid with three soft rubber pads under the 

 claws. Two solid brass jjillars support the trunnion axis on which the 

 limb inclines, and milled screws are on the ends of this axis for 

 tightening the motion. The coarse adjustment is by rack and pinion 

 moving a long prismatic slide attached to the body, and arranged to 

 compensate for wear. 



The substage for receiving accessories of English standard size 

 has two revolving diaphragms, one of the latter belonging to the con- 

 denser, all attached to the swinging mirror-bar, the axis of which is 

 fixed in the plane of the object, so that the diaphragm and mirror 

 swing concentrically around it. The mirror as well as the substage 

 can be moved on the mirror bar to and from the object, and both can 

 be removed, the latter by a prismatic slide. 



Since the figure was made, a modification of the stage-fitting per- 

 mits the swinging mirror-bar and substage to be swung above the 

 stage for the illumination of opaque objects. An auxiliary ring, with 

 internal " Society " screw is supplied for use in the substage, so that 

 objectives may be used as condensers. 



An immersion condenser, mounted in brass, fits either in the stage 

 or substage. It consists of a truncated cone of crown glass, with a 

 convex base, designed to focus the illumination upon the object. 



The glass stage and slide-holder are described infra. 



The chief point of novelty to us is the fine adjustment, which is 

 so simple and effective that we show it in detail in Fig. 5. The 

 drawing of the mechanism is made from Mr. Crouch's stand (Fig. 7) 

 in which the fine adjustment is similar. Messrs. Bausch and Lomb 

 hold a patent for this system of focussing in the United States. 



It will be seen that the solid bar A, carrying the optical body B, 

 is suspended on the front ends of the two broad, flat, parallel, tempered 

 steel springs CC, the other ends of which are attached to the limb D. 

 The pressure of the focussing-screw E, by the point at F on the solid 

 bar, forces down this bar, the springs bending sufficiently to allow 

 about ^ inch range of motion downwards from the normal position 

 (as figtired). The actual motion of focussing displaces the optic axis 

 slightly, as with the system adopted by Seibert and Kraflft (figured 

 and described ante, iii. (1880), p. 1047). But this displacement is of 

 no practical moment, except where the Microscope is provided with a 

 rotating stage, or where certain delicate micrometrical measurements 

 are required. This focussing must be regarded as practically free 



* See this Journal, iii. (1880) p. 1055. 



