THE MICROSCOPE AND ITS PARTS. 27 



clips, and the low-power objective used. The ripe seeds 

 of wild plants are easily studied in this way, and some 

 of them are marvellously beautiful. Small insects can 

 also be looked at when dry, but the result is not always 

 entirely satisfactory unless they are viewed as opaque 

 objects. Usually most objects appear better and show 

 more of their structure if examined under a disk of thin 

 glass and surrounded by water. But seeds, scales from 

 butterfly's wings, and many other things, can be viewed 

 and preserved in a dry state by enclosing them in a cell 

 with a thin glass cover fastened above. This " cell " 

 and "cover" and fastening process will be described 

 presently. 



All plants and animals living in water must be ex- 

 amined in water. To dry them and expect to learn 

 anything about them, or even to obtain a correct idea 

 of their true appearance, is a waste of time, and worse. 

 When your wet specimens get dry on the slide, and you 

 think you are seeing some wonderful things, add a drop 

 of water, and save yourself a probable blunder. Cer- 

 tain objects, naturally dry, will look better and will re- 

 veal their secrets sooner if examined wet. This is due 

 to optical reasons not necessary to explain here. The 

 observer, if he is seeking information, and not merely 

 pretty things to please the eye and the aesthetic fancy, 

 will do well if he examines naturally dry objects both 

 in and out of water; but things naturally wet must 

 never be seriously studied in a dry condition. 



The most convenient size for slips is three inches in 



