100 MICROSCOPIC OBJECTS. 



as tests of the penetrating and defining powers of this 

 instrument we may justly attribute the grand and mag- 

 nificent improvements which the microscope has recently 

 received. 



" Before entering upon my subject, it will be proper 

 to animadvert upon an error common to those who com- 

 mence the study of microscopic subjects. To set out 

 as they imagine fairly, they order an instrument to be 

 so constructed as to show the various subjects of amuse- 

 ment of the larger kind, as aquatic larvss, Crustacea, 

 beetles, cuttings of wood, scales of fish, wings, legs, &c. of 

 insects, and numerous other objects of this class ; and 

 at the same time the microscope is expected to exhibit 

 in perfection all the delicate minutiae in the structure of 

 tissues, hair, blood, the organization of animalcules, the 

 mosses, confervse, and the scales of the insects of the 

 orders Lepidoptera, Thysanura, 8^c. Now as this is 

 almost impossible, (at least I can aver that I never yet 

 saw one that was perfect in aU these departments ; and 

 this position will I think be found correct, until systems 

 of achromatic object-glasses of two, three, and four 

 inches focus shall be made equally perfect with the 

 deeper ones in all respects,) it is better to select an in- 

 strument that is efficient for those objects which are the 

 immediate subject of our study, and to get it as nearly 

 so in other respects as the constructions will admit. It 

 is true, that in the single and double microscope, and 

 also in the compound microscope, or engiscope, this can 

 ]De very well accomphshed by the addition of a number 



