32 The Microscope. 



linear measure. Thus the wing represented at fig. 4, 

 being magnified five diameters, is magnified twenty- 

 five times by superficial measure, and the object repre- 

 sented at fig. 6, and described as being magnified 420 

 diameters, occupies a hundred and seventy-six thou- 

 sand four hundred times more space than that of the 

 minute structure itself. But the " linear measure" is 

 in every way the best and most convenient method of 

 stating the magnifying power employed. 



The observer, after examining such an object as 

 this earwig's wing with a magnifyiug-glass, will do 

 well to submit it next to the lowest power of the com- 

 pound microscope, when probably some minute details 

 may appear demanding still further magnifying. A 

 power of a hundred diameters in a good microscope is 

 one which exhibits a great deal. The little folded 

 wing, fig. 1, d, is nicely shown with it ; its nineteen 

 folds may be seen squarely and neatly laid over each 

 other ; you reckon them as a shopman does the yards 

 of silk in a folded piece. Then, see the wing itself 

 with this power, you find it covered with very minuto 

 round marks, and fringed round with fine hairs. 



Beetles do not fold up their wings into so small a 

 compass as those of the earwig, and accordingly tho 

 strong ribs or nervures are differently arranged. No. 

 5 represents the folded-up wing of the whirligig beetle 

 (Gyrinus natator], a little water-insect, remarkable for 

 its habit of whirling round on the surface of ponds 

 and brooks.* This wing, when expanded, appears as 

 in fig. 4, Plate II. With this low magnifying power 

 * A figure of this beetle will be found in Chapter VII. 



