POWDERED VEGETABLE DRUGS 



--e 



movable stage capable of receiving various attachments, a mirror 



capable of being set in any direction, and a bull's-eye condenser. 



Dellabarre's microscope was, doubtless, superior to the preceding and 

 more complete in its construction. The ocular 

 was composed of six lenses, the objective of three 

 lenses, a plano-concave adjustable mirror and a 

 substage condenser. Dellabarre claimed achroma- 

 tism for his microscopes, but that was, perhaps, 

 only partially true. Later he reduced the number 

 of lenses employed. Fig. 5 shows the mechanical 

 parts, excepting the foot or base. A point worthy 

 of note is that as the simple and compound micro- 

 scopes increased in scientific value plainness of 

 construction superceded the evidences of decora- 

 tive fancies. Scrolls, conventional designs, etc., 

 were omitted, and the mechanical construction 

 was more effectually suited to the optical require- 

 ments. During the last half of the eighteenth 

 century some very ornamental instruments were 

 made, of which Martin's (1780) compound micro- 

 scope was a good example; but in spite of their 

 highly artistic finish they were, as a rule, very de- 

 fective optically. 



The highest magnification of the simple micro- 

 scope possible with a maximum correction of 

 spherical and chromatic aberration was not suffi- 

 cient to enable scientists to carry on efficient 

 histological investigations. Most of the com- 

 pound microscopes in use up to 1800 or perhaps 

 FIG. 3. Janssen's 1825, were in reality inferior to many of the simple 



compound microscope microscopes. It is true they gave a higher ampli- 

 fication, but this apparent gain was more than 



a ocular tube; 6, neutra n ze d by the increase in distortion and a de- 

 ocular lens; c, outer , . . 



tube; d, diaphragm- e crease m clearness of image due to chromatic and 

 middle sliding tube; f, spherical aberration. 



objective lens; g, lower Good compound microscopes have been in use 

 slkling tube; h, dia- f or nearly seventy-five years, but they have not 

 been extensively employed by students of phar- 

 macy for more than about thirty years. The 

 reason why they were not used earlier is, doubtless, to be found in 

 the fact that pharmacy as an independent science is of comparatively 

 recent origin. In the United States it is only within a few years that 





