A HOME-MADE TELESCOPE. 87 



ten thicknesses of paper will form a tube sufficiently thick and firm 

 for our purpose ; but only three or four layers should be laid at one 

 time, and, when these are dry, three or four more may be added, and 

 so on, until the requisite thickness is attained. When thoroughly dry, 

 which will be in three or four days, you will have a stiff, straight, 

 and light tube, the ends of which must be neatly and squarely cut off 

 with a sharp knife, so as to leave it, when finished, exactly twenty- 

 eight inches long. With a bit of sponge tied on the end of a stick, 

 and some common or India ink, black the whole inside of the tube, and 

 set it aside, on end, until the other parts are ready. 



Next form a tube on the smaller roller, with only four or five 

 thicknesses of paper, fifteen inches in length. When this is dry, pro- 

 ceed to form a third tube, over this second one as a roller, using six 

 or seven thicknesses of paper in its formation. This last is to be used 

 as a draw-tube for focusing with, and must be cut neatly and squarely 

 off at the ends to a length of fifteen inches. A portion of the inner 

 tube on which this was formed will be required for the eye-piece, 

 directions for making which I shall give further on. Blacken the in- 

 sides of both tubes, and set them aside, on end. 



One more tube is required, viz., that in which the draw-tube shall 

 slide. It needs to be only six inches long, but, in order to smooth 

 working, should be lined inside with fine cloth or cotton-velvet. Pro- 

 cure, therefore, a piece of black broadcloth, six inches long, and of 

 sufficient width to fit easily and accurately around the draw-tube. 

 Then, using the latter as a roller, first neatly fit the cloth thereon as a 

 first layer ; next paste or gum the back of the cloth, and, with this for 

 the innermost layer, form a short tube, six inches long, with paper and 

 paste, as before directed, using here not more than six thicknesses. The 

 draw-tube will now be found to move easily and smoothly back and 

 forth in this cloth-lined sheath ; but, for fear that the gum or paste 

 should have penetrated the cloth lining, and should stick the tube 

 and its sheath together, it will be safer to draw them apart before 

 drying, and thus save needless trouble and annoyance. 



On comparing the external diameter of this sheath with the in- 

 terior diameter of the large tube first made, it will be found that 

 some packing is required, to hold the former steadily and concen- 

 trically within the latter. Take, therefore, some three-quarters inch 

 strips of brown paper, and, having pasted them, wind around the 

 sheath at each end, to form rings or collars of equal thickness, and 

 large enough to fit snugly within the main tube. The appearance of 

 the sheath when completed will be as shown in Fig. 1, where a a' are 

 the collars just described. 



Now take the compound object-glass, consisting of a double-convex 

 crown-glass lens, A (Fig. 2), and a plano-convex flint-glass lens, B. 

 They will come from the optician's shop separate, but loosely fitted 

 into each other. Be careful to see that their several surfaces are bright 



