246 THE AMERICAN MONTHLY [Aug, 



sors point again. Awkward as it appears, I succeeded best with 

 the scissors. Brush the wax ofT clean and by means of a camel's 

 hair pencil brush the etching fluid into the sunken numbers. 

 After ten minutes the numbers will be marked into the glass ; 

 but better let stand over night, as a faint line will then be 

 marked quite distinct. Scrape and wash off" the wax and 3'()U 

 will have a $1 percolating jar. — Western Druggist. 



A Large Microscope, constructed especially for Bac- 

 teriological Studies. — This instrument was invented by Dr. 

 Roux and is manufactured by M. Stiassnie, successor to Ver- 

 ick, 43 Rue des Ecoles, Paris, France. It is constructed as sol- 

 idly as possible, and furnished with all the useful accessories. 

 The arrangement of the foot gives lightness and elegance to the 

 instrument and at the same time assures great steadiness in all 

 positions. The tube can be inclined, by means of a catch, to 

 the horizontal position. It is provided with a fine adjustment, 

 on a prism and a micrometer screw, and with a disc graduated 

 into fifty parts, by means of which sections one one-hundredth 

 of a millimeter in thickness can be measured, and this turns 

 before a movable index. 



The stage is circular, about six inches in diameter, and is of 

 unpolished ebony. It can be exactly centred by means of two 

 milled screws, placed on either side at the back of the stage. 

 The movement of these screws is sufficient to admit of bring- 

 ing the object into the field of the microscope when the highest 

 powers are used, and thus forms a kind of movable stage. 

 This stage is of sufficient size to admit of examining conveni- 

 ently isolated colonies in the Petri dishes and upon large-sized 

 slides. 



The sub stage and the mirror are moved vertically and sim- 

 ultaneously by a track and pinion. The sub-stage is mounted 

 uj^on an eccentric and is throvvn out toward the right from the 

 axis. It is made for using either the Abbe illuminator or the 

 ordinary diaphragm. Furnished with a spring which is at- 

 tached to a steel rod fastened to the under side of the stage at 

 the left, it can be turned back on its axis and retain its exact 

 centre during the movement. 



The iris diaphragm, of 32 millimetres, is mounted upon an 

 eccentric fastened to the sub-stage, and also is centered by a 



