OTHER USES OF LENSES 401 



own pictures rather than send them to a photographer, 

 for it is easy, and a fascinating pastime. Papers are of two 

 types, those printed by artificial light and those printed 

 by sunlight; the latter require more time and a dark 

 room. Blue printing paper is one form of sun printing 

 paper, which is much cheaper and easier to handle, since 

 we merely have to print from a negative, and then wash 

 in cold water. Chemicals for printing and developing can 

 be found in any good photographic shop and directions for 

 their use in any good manual. 



Enlarging. If you have a particularly good picture, 

 you may wish to enlarge it. This can be done by mak- 

 ing a positive image or picture by allowing rays of light to 

 pass through a negative, then through a lens which is 

 focused on a sheet of sensitive bromide paper. The size 

 of the enlargement will depend on the distance of the lens 

 from the sheet. It is not difficult to enlarge if one has a 

 room which can be darkened, and has a little ingenuity 

 so that he can make a frame to hold the bromide paper. 

 Enlargements are much more artistic because of their 

 softer tone, and make excellent presents. 



Other uses of lenses. We are all familiar with the use 

 of the opera glass and field glass. A good pair of field 

 glasses apparently decreases the distance of the object 

 looked at to one eighth of the real distance. A four-inch 

 telescope may make an object appear one three-hun- 

 dredth of its distance. In the telescope, one lens is used 

 to make an image of the distant object, and the second 

 lens, the eyepiece, is used as a simple microscope which 

 magnifies this image. If you can get the use of a good 

 field glass or small telescope, look at the moon in its differ- 

 ent phases. You will find it a most interesting object for 



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