4 The Microscope. 



of lenses) is fixed to a stand of any kind ; and in its 

 complete form it should have a little plate of metal, c, 

 No. 1, called the stage, on which the objects are 

 placed; a mirror, d, to throw light on the objects from 

 below ; and a condensing lens, e, for the illumination 

 of objects from above. Probably there will be a screw 

 head fixed to rackwork for bringing the lens to the 

 correct distance required for showing the object clearly. 

 There will also be various useful pieces, of apparatus, 

 as a pair of forceps, a box for holding minute live 

 things, some slips of glass, etc. And there will be 

 two or three different lenses, which can be used either 

 separately or screwed together, giving good variety of 

 magnifying power. The lowest power of such a 

 microscope would show the " earwig's wing" slightly 

 larger than at fig. 2, Plate II., and the highest might 

 nearly reach the magnifying power shown at fig. 9 in 

 the same Plate. Even a higher degree of magnifying 

 is attained by an ingenious combination of lenses; 

 but the performance of even the best of these Jiigli 

 powers of the simple microscope is unsatisfactory, 

 compared to the corresponding power of the compound 

 microscope ; and for still greater magnifying the latter 

 instrument alone supplies our need. 



The difference between its principle and that of 

 the simple microscope should now be explained. In 

 the simple microscope we look directly at the object, 

 with the lens close to the eye ; but in the compound 

 microscope we use the lens to look, not at the object, 

 but at an image formed ly another lens placed furthest 

 from our eye, and next to the object ; that image is 



