NACHET'S MICROSCOPES. 



Fig. 44. 



two prisms fixed at B B' in the tubes, which are placed at right 



angles to the lower prism A ; by this 



second reflection, the reversed image of 



the first reflection, being again reversed, 



is made to correspond with the natural 



position of the object. 



91. An interesting variety of this form 

 of instrument, which may be called a 

 BINOCULAR MICROSCOPE, is shown in 

 fig. 44. In this case the two tubes, B c 

 and B' c', containing the two eye-pieces, 

 are placed parallel to each other, the 

 distance between them being regulated 

 by the screws v v ; if this distance be 

 so adjusted as to correspond with the 

 distance . between the eyes of the same 

 individual, the microscope may be used 

 with both eyes, in the same manner as 

 a double opera-glass. This has the 

 advantage of giving a stronger ap- 

 pearance of relief to the objects viewed, 



which is especially desirable for a certain class of objects, such as 

 crystals. 



92. A triple microscope, upon the principle above described, is 

 shown in fig. 45, p. 81, where A is the object-piece, B the multiple 

 prism, and c, c' and c" the three eye-tubes. 



A similar instrument, with four eye-tubes, including figures to 

 illustrate the mode of observing with it, is shown in fig. 46, p. 33. 



One of the advantages of this class of instruments is, that a 

 professor and one or more of his pupils may view the process of a 

 microscopic dissection which with a common microscope would be 

 impossible, and to which the solar microscope would be inap- 

 plicable. Microscopic dissections, in general, can only be exhibited 

 to those who do not execute them, by their ultimate results. Any 

 phenomena which are developed in their progress, can only be 

 made known to others by description ; and it is not necessary to 

 say, how imperfect such a mode of communication must be, com- 

 pared with direct observation. 



