248 



But as it is sometimes necessary or convenient that the object 

 should be placed horizontally and the microscope-tube vertically, — 

 as in examining fluids with low powers, or opaque bodies, — certain 

 additions have been made to this model to render it capable of 

 being so used ; reflected light, or the use of the condensing lens 

 being substituted for the mode of illumination for which it is 

 specially adapted. This, of course, involves the expense of a 

 mirror and lens with their adjustments, which is, however, tri- 

 fling, if the plan here shown is followed. 



The instrument is represented in working order in figure 1. 



The base of the whole is a box made of black walnut, three 

 quarters of an inch thick, having two uprights, of the same mate- 

 rial and thickness, firmly screwed to the inner edges of the strips 



