28 



THE AMERICAN MONTHLY 



[Jan., 



ogy;" Lord Ray leigh's consideration of "The New Element in 

 the Atmosphere ; " on " The Elseviers; " The Railroad in Asia;" 

 and an account of " The World's Cables ; " The "■ Reviews," is 

 a new and important addition to the magazine. 



MICROSCOPICAL APPARATUS. 



Prof. Gage's Marker. — A preliminary notice of this instru- 

 ment was furnished on pp. 337-339 of The Journal, forNovem- 

 ber, 1894, but without the figure and description given below. 



Fig. 1, is the entire marker in section showing the details of 

 construction. SS is the upper part with society screw for insertion 

 into the nose-piece of the microscope like an objective. R is 

 the lower or revolving part carrying the brush, B. C is a mov- 



55 



able cylinder by which the brush is made more or less eccen- 

 tric. MM are milled rings on the society screw and the revolv- 

 ing parts. S is a screw connecting the two parts of the marker. 

 The dotted line represents the position of the axis of the marker. 



Fig. 2, lower end of the marker turned around' 90 degrees to 

 show the manner of insertion of the movable cylinder carrying 

 the brush, B. S isa set screw for tightening the movable cylin- 

 der. 



Figures 3 and 4, consist of slides illustrating the use of the 

 marker. Pig. 3, is an ordinary circular cover with a ring show- 

 ing where the part showing especiall}'- well may be found. 

 Fig. 4, is a slide with a series of rings. The ringed section is 

 the one showing a special structure most clearly. 



