44 Things not generally Known. 



signers and draughtsmen may improve and help their fancies. 

 They must choose two pieces of looking-glass of equal bigness, 

 of the figure of a long square. These must be covered on the 

 back with paper or silk, to prevent rubbing off the silver. This 

 covering must be so put on that nothing of it appears about the 

 edges of the bright side. The glasses being thus prepared, must 

 be laid face to face, and hinged together so that they may be 

 made to open and shut at pleasure like the leaves of a book." 

 After showing how various figures are to be looked at in these 

 glasses under the same opening, and how the same figare may 

 be varied under the different openings, the ingenious artist thus 

 concludes: " If it should happen that the reader has any num- 

 ber of plans for parterres or wildernesses by him, he may by this 

 method alter them at his pleasure, and produce such innumer- 

 able varieties as it is not possible the most able designer could 

 ever have contrived." 



MAGIC OF PHOTOGRAPHY. 



Professor Moser of Konigsberg has discovered that all bo- 

 dies, even in the dark, throw out invisible rays ; and that these 

 bodies, when placed at a small distance from polished surfaces 

 of all kinds, depict themselves upon such surfaces in forms 

 which remain invisible till they are developed by the human 

 breath or by the vapours of mercury or iodine. Even if the 

 sun's image is made to pass over a plate of glass, the light 

 tread of its rays will leave behind it an invisible track, which 

 the human breath will instantly reveal. 



Among the early attempts to take pictures by the rays of the sun 

 was a very interesting and successful experiment made by Dr. Thomas 

 Young. In 1802, when Mr. Wedgevvood was " making profiles by the 

 agency of light," and Sir Humphry Davy was " copying on prepared 

 paper the images of small objects produced by means of the solar micro- 

 scope," Dr. Young was taking photographs upon paper dipped in n so- 

 lution of nitrate of silver, of the coloured rings observed by Newton ; 

 and his experiments clearly proved that the agent was not the luminous 

 rays in the sun's light, but the invisible or chemical rays beyond the 

 violet. This experiment is described in the Bakerian Lecture, 1803. 



Niepce (says Mr. Hunt) pursued a physical investigation of the cu- 

 rious change, and found that all bodies were influenced by this principle 

 radiated from the sun. Daguerre* produced effects from the solar pencil 

 which no artist could approach ; and Talbot and others extended the 

 application. Herschel took up the inquiry; and he, with his usual 



* Some time before the first announcement of the discovery of sun-painting', 

 the following extract from Sir John Herschel's Treatise on Light, in the Encyclo- 

 pcediaMrtropolitana, appeared in a popular work entitled Parlour Magic: " Strain 

 a piece of paper or linen upon a wooden frame, and sponge it over with a solution 

 of nitrate of silver in water; place it behind a painting upon glass, or a stained 

 window-pane, and the light, traversing the painting or figures, will produce a 

 copy of it upon the prepared paper or linen ; those parts in which the rays were 

 least intercepted being the shadows of the picture." 



