182 DISSERTATION SECOND. [part i. 



it in a work, entitled Magia Naturalis. The light was 

 admitted through a small hole in the window-shutter of a 

 dark room, and gave an inverted picture of the objects 

 from which it proceeded, on the opposite wall. A lens 

 was not employed in the first construction of this appara- 

 tus, but was afterwards used ; and Porta went so far as to 

 consider how the effect might be produced without inver- 

 sion. He appears to have been a man of great ingenuity ; 

 and though much of the Magia Naturalis is directed to 

 frivolous objects, it indicates a great familiarity with ex- 

 periment and observation. It is remarkable, that we find 

 mention made in it of the reflection of cold by a speculum, ' 

 an experiment which, of late, has drawn so much attention, 

 and has been supposed to be so entirely new. The cold 

 was perceived by making the focus fall on the eye, which, 

 in the absence of the thermometer, was perhaps the best 

 measure of small variations of temperature. Porta's book 

 was extremely popular ; and when we find it quickly trans- 

 lated into Italian, French, Spanish, and Arabick, we see 

 how much the love of science was now excited, and what 

 effects the art of printing was now beginning to produce. 

 Baplista Porta was a man of fortune, and^is house was so 

 much the resort of the curious and learned at Naples, that 

 it awakened the jealousy with which the court of Rome 

 watched the progress of improvement. How grievous it 

 is to observe the head of the Christian church in that and 

 the succeeding age, like the Anarch old in Milton, reign- 

 ing in the midst of darkness, and complaining of the en- 

 croachments which the realm of light was continually 

 making on his ancient empire ! 



The constitution of the eye, and the functions of the 

 different parts of which it consists, were not yet fully un- 



1 Magia Naturalis, Lib. 17, cap. 4, p. 583. Amsterdam edit. 

 1664. 



