OPTICAL INSTRUMENTS. 



185 



in coming in, only in a different direction. Place the box so 

 that a pencil of light falls directly on the convex glass, at 

 the end : as soon as water is poured in the box, the rays 

 converge and meet in a point ; cause the pencil of light to 

 fall on the concave glass, and the rays diverge, and the 

 pencil of light is enlarged. Many other experiments illus- 

 trating refraction, and the passage of light through lenses, 

 may be illustrated in a beautiful manner by this instrument. 



Price, $4.00 and $5.50. 



The Optical Diagonal Ma- Fi e- m - 



chine, Print Glass, or Cosmo- 

 ramma (Fig. 701), consists of 

 a convex lens from four to six 

 inches in diameter, mounted in 

 a square frame, and supported 

 by an ornamental framework 

 resting on a round pedestal, in 

 the column of which is a slide, 

 and a screw to fix it any height 

 required to view the print with 

 the best effect; behind the 

 lens is a frame, with a mirror 

 considerably larger than the 

 lens, which is jointed at the 

 top, and may be supported at 

 a proper angle by a wire for 



the purpose. The prints are laid on the table, and viewed 

 in the mirror through the lens, producing a very deceptive 

 appearance, and in imagination bringing the reality before 

 you. The frame is of polished wood, and may be taken 

 apart by unscrewing for convenient transportation. 



This instrument, used for magnifying prints, is neat in its 

 appearance and useful in its application ; pictures are very 

 interesting to children, and give them a very just idea of the 

 relative size and distance of objects ; they also teach them 

 accuracy of sight, engage their imagination, and fix their 

 attention, promoting many inquiries, which, if judiciously 

 answered, will store their minds with useful information. 



Good perspective views designed for this instrument, 



handsomely colored, fourteen inches by twenty-two in size, 



embracing views of many of the most celebrated public 



buildings of the principal cities in Europe, interiors of public 



16* 



