1014 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Societies, &c. (fig. 238) ; (3) as a field Microscope and class demonstration 

 instrument (fig. 239). 



The instrument has two objectives, a 4/10 in. and a 1 in., which, with 

 two eye-pieces, give the following powers: — 35, 70, 100, 200. The 4/10 is 

 of * 65 N.A. The highest power, therefore, is equivalent to a 1/2 in. of 



Fig. 239. 



80° with a C eye-piece, or a 1/4 of 80° with an A eye-piece, on an ordinary 

 full-sized English Microscope. The lowest eye-piece is on the Abbe 

 compensating principle. 



In the mechanical portion of the instrument are several new features. 

 The design of the Microscope is that which is generally known as the bar 

 movement. It has a rack-and-pinion coarse-adjustment, and no fine-adjust- 

 ment, thereby following the dictum of the great master (the late Hugh 

 Powell), who said, " In an elementary Microscope a good coarse-adjustment 

 without any fiue is better than one with a second-rate fine and no coarse- 

 adjustment." The truth of this statement is daily verified in the shaky 

 condition of the fine-adjustments of students' Microscopes which are fitted 

 with a direct-acting screw fine-adjustment and a sliding-tube coarse-adjust- 

 ment. The body of the Microscope is 3 inches long. The stage is of 

 Mr. Nelson's horseshoe pattern, and the spring clips are those of Hugh 

 Powell. Although strongly opposed to all kinds of clips, Mr. Nelson found 

 they were necessary in this instance to permit of the complete inversion of 

 the instrument. The great difference between these clips and those of the 

 usual form is that these being fixed underneath the stage, allow a smoothness 

 of action to the slip which is totally foreign to the others. 



To the underneath side of the stage is fixed the substage which carries 

 an achromatic condenser, focusing by means of a sliding-tube. 



The stage and substage rotate on an axis, so that they may be turned 

 into the plane of the trunk for packing. 



There is a plane mirror mounted on a crank arm. The foot is circular, 

 rests on three points, and has an upright rod capable of extension like a 



