««•. v.] DISSERTATION SECOND. l8i 



ceased to be so thinly scattered over the wastes of time. 

 Maurolycus, whose knowledge of the pure mathernaticks 

 has been already mentioned, was distinguished for his skill 

 in opticks. He was acquainted with the crystalline lens, 

 and conceived that its office is to transmit to the optick 

 nerve the species of external objects ; and in this process 

 he does not consider the retina as any way concerned. 

 This theory, though so imperfect, led him nevertheless to 

 form a right judgment of the defects of short-sighted and 

 long-sighted eyes. In one of his first works, Theoremata 

 de Lumine et Umbra, he also gives an accurate solution 

 of a question proposed by Aristotle, viz. why the light of 

 the sun, admitted through a small hole, and received on a 

 plane at a certain distance from it, always illuminates a 

 round space, whatever be the figure of the hole itself, 

 whereas, through a large aperture, the illuminated space 

 has the figure of the aperture. To conceive the reason 

 of this, suppose that the figure of the hoie is a triangle ; it 

 is plain that at each angle the illuminated space will be 

 terminated by a circular arch of which the centre corres- 

 ponds to the angular point, and the radius to the angle 

 subtended by the sun's semidiameter. Thus the illumi- 

 nated space is rounded off at the angles ; and when the 

 hole is so small that the size of those roundinss bears a 

 large proportion to the distance of their centres, the figure 

 comes near to a circle, and may be to appearance quite 

 round. This is the true solution, and the same with that 

 of Maurolycus. The same author appears also to have 

 observed the caustick curve formed by reflection from a 

 concave speculum. 



A considerable step in optical discovery was made at 

 this time by Baptista Porta, a Neapolitan, who invented 

 the Camera Obscura, about the year 1560, and described 



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