12 



THE BRITISH NATURE BOOK 



FIG. 7. 



It is hardly necessary to point out how to focus the object. The telescope 

 tubes must be slid downwards towards the object, which is observed all the 

 time through the eyepiece, until it is perfectly sharp and clear. In focusing 



with both tubes extended, take care to focus with the 



ll) J fii" * lower tube, and not the upper. 



\^=/ US A great many objects perhaps the first to be 



examined by the young microscopist are opaque, and 

 therefore cannot be lighted by transmitted light 

 that is, by light thrown from the mirror below them. 

 Instead, light must be concentrated upon them from 

 above. For this purpose a condenser is necessary, 

 and this, like the rest, is easily and cheaply made. 

 Figs. 7 and 8 show two roughly made condensers, the lens of which is a 

 bull's-eye, obtained at a cycle shop for a few pence. In Fig. 7 it is shown 

 mounted in a block of wood. The rest of the apparatus consists of a hat-pin, 

 a knitting needle, a cork, and a block of wood. With this the condenser 

 can be moved and rotated vertically or horizontally, and set at any angle, 

 and so will cast the rays of light from a lamp in a concentrated spot upon 

 the object under the microscope. It will be found that the condenser 

 must be two or three inches away from the object. 

 The second form (Fig. 8) shows the lens mounted 

 in a penny candle-shade holder, supported on a rod 

 of wood stuck into a lump of plasticine. It needs 

 no further description. 



A few slips of glass are required upon which to 

 place the objects under observation. These should 

 be 3 inches by i inch the standard size. They 

 can be cut from disused quarter-plates, the glass 

 used in photographic plate manufacture being very 

 thin and free from flaws. 



I venture to add that details as to simple mounting and preparing of objects, 

 and all other necessary information as to the use of a simple microscope, can 

 be found in The Young People's Microscope Book. 



A Simple Nature Camera. 



" Buy an 'am and see life," says Kipling's Mr. Pyecraft ; and it will 

 appear to some of my grown-up readers as if I were parodying the advice and 

 saying, " Buy a cheap telescope and see Nature " : for once again I propose 

 to show how to use the " object lens " of the telescope as a photographic lens 

 in a simple home-made camera. 



I am not going to pretend that this lens will be of any use for instantaneous 

 photography though it could be so used, provided it was fitted into an in- 

 stantaneous shutter ; but as this would involve more expense, I propose that 



