POPULAR ASTRONOMY. 



123 



oscillate freely about the boll as a cen- 

 ter. A large steel nail (d) Fig. 4, five 

 inches long, is driven into the under side' 

 of the block and the head is removed. 

 Two clothes hooks are screwed into each 

 of the wooden pieces (E) Fig. 4, near 

 the end ; a short cylinder ( p ) of heavy 

 pasteboard is tied to the pieces and is 

 held in place by the clothes hooks. The 

 telescope tube is to be inserted in this 

 cylinder as shown in the photograph. 

 A movable block (o) Fig 5, is held in a 

 box (k) Fig. 5, by a clamp (h) Fig. 5, 

 and three oak strips (m) Fig. 5, are se- 

 curely fastened to the box. One strip 

 may be arranged (n) Fig. 5, so that it 

 can be removed, if it is found more con- 

 venient. The nail (d) Fig. 4. is inserted 

 in the hole (11) Fig. 5, and provides the 

 horizontal movements of the telescope. 

 With a double convex or a meniscus 

 lens, the full aperture will be used only 

 in looking at stars and nebula? ; the plan- 

 ets, sun and moon are best seen when a 



diaphragm is placed before the lens. 

 ( )rdinarily, the aperture should be less 

 than two inches, but it is well to try sev- 

 eral sizes. 



A thick piece of dark glass can be fixed 

 over the eye lens, to make a solar eye- 

 piece ; but the best way to observe the 

 transits or sun spots, is to point the 

 telescope at the sun through a hole in 

 the window curtain. A very large 

 image of the sun can be projected upon 

 a white screen in a darkened room. 



We can see some of giant Jupiter's 

 belts, and can watch, with much inter- 

 est, the changing positions of his four 

 moons. The phases of Venus and the 

 rings of Saturn are interesting objects 

 for our glass. The moon affords the 

 most pleasure, when the conditions are 

 favorable for the best "seeing." With 

 a realism that is startling, the craters, 

 walled plains, and the bright glowing 

 mountain peaks stand out, in strong con- 

 trast from their black shadows. 



"Position 

 of the eye- 



A-f 



Ficr 4. 



DIAGRAMS TO SHOW CONSTRUCTION. 



