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VISUAL INSTRUCTION. 



ArniTORIUM IN Ml'SETM OF NATURAL HISTORY, SHOWING SPECIAL GALLERY FOR LANTERNS. 



projected upon a white screen or background in 

 a dark room by moans of a stereopticon. This 

 picture is magnified many times so that it can 

 be seen in minutest detail by the class or audi- 

 ence. Visual instruction is not a new method of 

 imparting knowledge, but it is now carried to such 

 perfection, and is found so helpful in the study of 

 science, history, travel, and domestic economy, 

 that it is worthy to be termed an art. 



The Pictures. A photographic negative of the 

 object to be studied is first made, from which a 

 positive is printed upon a prepared glass 3} by 4 

 inches in size. The glass for these positives must 

 be clear and bright to give the best results. All 

 objects covered by the picture will appear in light 

 and dark shades, showing upon the canvas with- 

 out color, but these positive pictures may be so 

 tinted by a skillful artist that Nature will be re- 

 produced (piite accurately. Kspecially is this true 

 of landscapes, birds, mammals, and flowers. 



The Projecting Instrument. The primitive 

 method of projecting these pictures upon a screen 

 \\a* by means of the magic lantern, beginning with 

 its use as a mere toy, where a common oil lamp 

 was employed for a light, and coming by degree- 

 to the use of the stercopticon, single, double, and 

 triple. The stereopticon consists of a case of 

 metal in which is placed the light, the con- 

 denser for concentrating the rays of light, the 

 lenses or object glasses for magnifying the pictured 

 object, and the -lidc holding the positive picture 

 in place. 



The Illuminator. The oil lamp can not be 

 made to throw a light strong enough to bring out 

 the pictures distinctly without the use of many 

 wicks and consequent imperfect combustion, im- 



parting a yellow color to the flame, and frequently 

 causing smoke annoying to the lecturer as well 

 as to the audience. House gas, by means of 

 the Welsbach burner, may be used in a parlor 

 or schoolroom, but the extreme delicacy of the 

 " mantle " employed prevents its general use as 

 an illuminator even as a stationary light. Acety- 

 lene gas is of recent use. and has been found to be 

 superior to oil light. The oxyhydrogen or lime 

 light projects a very clear, bright picture, and 

 is in common use for illumination in illustrated 

 lectures. The electric light is more intense and 

 penetrating than the lime light, and the mechan- 

 ism of the lamp has been so simplified and brought 

 to such a state of perfection that it is easily 

 manipulated, and that light is now used exclu- 

 sively at the American Museum of Natural 

 History. 



Other Methods. Visual instruction may be 

 imparted in other ways than by the use of the, 

 -tcrcoptieon. The microscope permits of the in- 

 vestigation of infinitesimal objects in Nature in 

 all their complicated structure and in their nat- 

 ural, variegated coloring, but only one person can 

 use the instrument at a time unless the microscope 

 be connected with the stereopticon. Thus few stu- 

 dents could become familiar with the natural ol>- 

 jects beyond their own immediate vicinity. For 

 the popular purposes of visual instruction the 

 stereopticon and the photograph have esfablished 

 themselves permanently in the principal educa- 

 tional centers. 



The American Museum of Natural History. 

 --The present standing of visual instruction and 

 its development are best shown as exemplified at 

 the American Museum of Natural History, of 



