THE MICROSCOPE AND ITS PARTS. 3 



every summer pool and disgusts him until his little 

 lens reveals its purity and its grace. The pocket-lens 

 is always ready for the exam- 

 ination of anything picked up 

 in the fields or woods, it is small, 

 and is easily carried in the pocket. 

 It can be obtained in a great f^s- — a Pooket-Uns. 



variety of shapes, so far as the frame that holds the 

 lens is concerned; it can be had with but one glass, or 

 with two or three of various powers, to be used alone 

 or combined; it can be bought with a large lens of low 

 power in one end of the frame, and a smaller glass of 

 higher power in the other. But whatever form the 

 beginner may select he should remember that the 

 larger the simple lens the lower, as a rule, will be the 

 magnifying power, and the longer the working-distance; 

 or the space between the glass and the object when in 

 focus; and the smaller the lens the more convex it will 

 be, the greater the power it will have, the shorter will 

 be the working-distance, and the less of the object it 

 can show at one view, and consequently the more 

 troublesome will be its use. The beginner is advised 

 to purchase a good pocket-lens with a working-dis- 

 tance, or "focal-length" as it is sometimes rather in- 

 correctly termed, ofx)ne or of one and one-half tii'Ches. 

 This is all that is really needed for the examination of 

 botanical specimens and of the thousand and one ob- 

 jects that attract the attention on every summer ram- 

 ble. 



The writer personally dislikes the combination pock- 

 et-lens formed of two or three separable glasses. If 

 but one lens of the combination is Wanted for immediate 

 use, the entire number must be pilS'h'ed' but' of -the thick 



