666 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Surirella linearis W. Sm. vr. ; S. nobilis W. Sm. c. ; NitzscMa linearis 

 W. Sm. vr. Family 10, Melosireae. Melosira nivalis W. Sm. = Cos- 

 cinodiscus Smithii vr. Family 15, Coscinodiscese. Gyclotella antiqua 

 W. Sm. c. Also a form that for want of better objectives Mr. Burgess 

 is unable to identify beyond that it is an Odontidiurn or Navicula. 



MICEOSCOPY. 



a. Instruments, Accessories, &c. 



Bausch and Lomb Optical Co.'s Professional Microscope.— Fig. 



113 (sent from America, and one of the best woodcuts of a Microscope 

 which we have seen) shows the "Professional" Microscope of the 

 above Company. 



Its specialities are the frictionless fine adjustment (described at 

 p. 683), the glass stage and slide-carrier (described at p. 687), the 

 centering of the substage (of which we have no detailed description), 

 the two draw-tubes which allow of more than the ordinary variations 

 of length, and the mirror and substage bars which are separate and 

 can be moved independently of one another, or simultaneously when 

 the arm on the mirror is placed in a recess in the substage bar. 



Bnlloch's Newer Congress Stand.* — This (Fig. 114) is made 

 upon the original plan,! with the exception of the stage, the con- 

 struction of which has been modified. 



The stage (Fig. 115, Nos. 1-4) is held by a saddle-piece which is 

 steadied by a strong brace passing down from the limb. It is entirely 

 independent of the swinging of the mirror and substage. This saddle- 

 piece contains a set of screws with perforated heads for centering the 

 ring which supports the stage. These screws are so far back that the 

 ring can be made very thin without reducing the strength or rigidity. 

 The stage rests upon this ring. It rotates, and can be accurately 

 centered by the screws in the saddle-piece. 



This stage is a revival of an idea which Mr. Bulloch says was used 

 by Spencer thirty years ago. It consists of the ordinary stage-plate, 

 having in its centre a large square hole. One side of this plate con- 

 tains a wide dovetailed groove, in which slides a bar with its surface 

 level with the top of the plate. At right angles to this bar is attached 

 another bar. On this second bar slides a third bar, into which it has 

 been dovetailed. The motion of this third bar is at right angles to 

 the motion of the first. A tbin plate is attached to the third bar, and 

 lies flat upon the stage-plate. This plate is perforated, and holds the 

 slide by means of a spring. It will be seen that this arrangement 

 permits of motion of the thin plate in two directions at right angles 

 to one another. Two pinions, perpendicular to the stage, control 



* Cf. 'National Scientific Journal,' i. (1881) pp. 230-1 (5 figs.). 

 t See this Journal, iii. (1880) pp. 1076-8. 



