8 



THE BRITISH NATURE BOOK 



FIG. 2. The objective at D 

 in Fig. i. 



is not a difficult matter to make a little wooden holder for them, if considered 



necessary. 



This fourth tube, called the " eyepiece," is really a small microscope, the 



two lower lenses in their mount being the " objective," the two upper ones the 

 true " eyepiece " ; and this is the portion we shall 

 use, later on, when we fit up our microscope as a 

 table instrument. Meanwhile, it is a delightful thing 

 to take the tube as it stands into the garden and 

 examine leaves, flowers, and insects with it. Holding 

 it about an inch from the object, you will find that 

 very slight movement to or from the object will bring 

 it into sharp focus. Fig. 3 shows how to hold an 

 object in one hand and the microscope in the other, 



and get a perfectly steady view three fingers of the left hand touching the 



lower edge of the right hand. 



Having thus dissected the telescope, fit it together again, taking care 



not to force the screwing, or the threads will be destroyed. If you give a light 



and easy turn to each section, you will find the screws bite almost at once ; 



when the process is complete, do not screw tight home, but use just sufficient 



pressure to make each screw-joint hold, and that is all. 



Now, as pointed out above, these telescopes are excellent for observation 



of distant objects, but they will not focus anything within fifteen feet of the 



observer. It must happen often that the Nature 



student would like to be able to watch insects 



and other small creatures at a much shorter 



distance a spider, for example, at work upon its 



web, aphides on the rose bushes, bees gathering 



honey, and so forth. With a very slight addi- 

 tion the telescope can be used upon objects as 



near as three feet. All that is required is a 



spectacle lens, placed in front of the object lens A. 

 The more powerful this additional lens is, the 



nearer you can get to the object ; but there is 



nothing to be gained by having this lens of a 



higher power than is actually necessary. I find 



that a spectacle lens of the power x i or x 0.5 



is ample. Opticians and spectacle makers have 



a large number of chipped lenses, which are use- 

 less to them, and these can be bought extremely 



cheaply I have bought many at the rate of six 



for a penny and there will almost certainly be found among them one or 



more of the strength required. The fact that they are chipped will not matter 



at all, as, in any case, you will have to take off the edges to make the lens 



fit. If you have no glazier's diamond, use a pair of pliers, and pinch off the 



FIG. 3. 



