LARGE MICROSCOPES| 37 



Group 2. Medium microscopes costing about 10. 



Group 3. Students' stands at about 5 or somewhat less. 



Large Microscopes. Six examples of the first-class 

 stands of different makers are given. The first three are 

 more elaborate than the others, and are fitted up 

 with all, or nearly all, the features that have been de- 

 scribed as desirable for photomicrography. They are 

 consequently more expensive than the microscopes 

 exemplified by the next three figures, and, with other 

 similarly complete instruments, cost between 20 and 

 30. The next three, Figs. 15, 16, and 17, deserve 

 equally well the name of first-class microscopes. 

 They do not suffer in comparison with those at 

 higher prices on account of any inferiority of work- 

 manship and finish, but they are not so complete in 

 their equipment, although fitted with every essential 

 for critical work. 



Swift's "Premier" (Fig. 12). In the design of this 

 microscope Messrs. Swift had the advantage of a specifi- 

 cation given by Mr. Barnard, and the result is an instru- 

 ment that may be given here as a model of what a photo- 

 micrographic stand should be. The " Wales " principle 

 of inclination, in which the limb slides round on the foot, 

 is adopted, and gives a stand that is equally rigid in both 

 horizontal and vertical positions. The foot is a very 

 substantial claw tripod. The tube is '2" in diameter, 

 and fitted with draw-tubes extending to 250 mm. The 

 mechanical stage permits of complete rotation, is 

 fitted with centring adjustment, and allows of the 

 systematic examination of the entire surface of a 3" x 1 \" 

 slide. The fine adjustment is of a very slow lever pattern 

 actuated by twin milled heads which are graduated. 



The substage is focussed by rack and pinion, and 

 centring screws are fitted to the ring into which the 

 condenser slides. There is an Iris diaphragm beneath it 

 with rack-and-pinion motion for oblique light. 



