100 MICROSCOPIC ILLUSTRATIONS. 



The above sets may be divided into three classes the 

 shallow, medium, and deep ; which, like the eye-pieces, 

 I shall particularize by the letters A, B t C. 



The shallow object-glasses. A, are mainly serviceable 

 for opaque objects, which, when exhibited by means of 

 silver specula of proper dimensions and curvature, yield 

 a vast fund of amusement and instruction. The class of 

 objects, enumerated under the eye-piece, A, is suitable 

 for them. They display to great advantage, also, the 

 aquatic larvae of insects, polypi, &c. They are service- 

 able as a finder for minute objects ; for the general 

 examination and selection of insects ; minute fossils ; 

 coal, &c. ; the objects thus selected being afterwards sub- 

 mitted to the medium object-glasses, B. 



Those denominated B, possessing considerable pene- 

 tration, bring out the striae and markings on the scales of 

 insects, the various forms of the elementary tissues and 

 fibres of vegetables, the internal structure of polypife- 

 rous zoophites ; whilst a general view of those minute 

 and delicate living creatures, the animalcula infusoria, 

 as also the circulation in the young of the lizard, aquatic 

 plants, &c., is obtained by the intermediate sets. The 

 medium-power object-glasses, when constructed with a 

 sufficient space in front, admit of a minute examination of 

 portions of insects preserved in Canada balsam between 

 plates of glass of the usual thickness. This class of 

 transparent objects, when mounted in the permanent 

 manner I have mentioned, is certainly the most instruc- 

 tive and amusing of any that we possess ; for although 



