76 SIXTEENTH CENTURY. pt. hi. 



You may perhaps have been into one at the sea-side, where 

 they build them for visitors to watch the coloured reflec- 

 tion of the passers-by. In the camera obscura, as it is now 

 made, the glasses are so arranged that the figures are up- 

 right. 



Porta saw at once how useful this invention would be for 

 making accurate drawings of objects ; for, by tracing out with 

 colours on the wall the figure of the man or tree as it stood, 

 he could get a small image of it with all its proportions and 

 colours correct. But, what is still more important, he was 

 led by this experiment to understand how we see objects, 

 and to prove that Alhazen was right in saying that rays 

 of light from the things around us strike upon our eye. 

 For, said Porta, the little hole in the shutter with the lens 

 in it, is like the little hole in our eye, which also con- 

 tains a natural convex lens ; and we see objects clearly 

 because the rays pass through this small hole. He did 

 not, however, know which part of our eye represents the 

 wall on which the figure is thrown, nor why we see objects 

 upright ; we shall see (p. 96) that Kepler discovered this many 

 years afterwards. 



When Porta had succeeded in getting clear images of 

 real things on the wall, he began to try painting artificial 

 pictures on thin transparent paper and passing them across 

 the hole in the shutter, and he found that the sun threw a 

 very fair picture of them on the wall. In this way he pro- 

 duced representations of battles and hunts, and so made a 

 step towards the Magic Lantern. He seems, however, never to 

 have tried it by lamplight ; this was done by Kircher, a Ger- 

 man, about fifty years later. There is no doubt that Porta had 

 a very good notion of how to use two magnifying glasses so as 



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