126 NOVUM OROANUM 



the angles of incidence are very obtuse, and the reflected 

 rays at a greater distance. In the meantime it must be 

 observed, that there may be many operations of the solar 

 rays, relating, too, to the nature of heat, which are not pro 

 portioned to our touch, so that, with regard to us, they do 

 not tend to produce warmth, but, with regard to some 

 other bodies, have their due effect in producing it. 



Let the following experiment be made. Take a lens the 

 reverse of a burning-glass, and place it between the hand 

 and the solar rays, and observe whether it diminish the heat 

 of the sun as a burning-glass increases it. For it is clear, 

 with regard to the visual rays, that in proportion as the lens 

 is made of unequal thickness in the middle and at its sides, 

 the images appear either more diffused or contracted. It 

 should be seen, therefore, if the same be true with regard 

 to heat. 



Let the experiment be well tried, whether the lunar rays 

 can be received and collected by the strongest and best 

 burning-glasses, so as to produce even the least degree of 

 heat. 16 But if that degree be, perhaps, so subtile and weak, 

 as not to be perceived or ascertained by the touch, we must 

 have recourse to those glasses which indicate the warm or 

 cold state of the atmosphere, and let the lunar rays fall 



18 Montanari asserts in his book against the astrologers that he had satisfied 

 himself by numerous and oft-repeated experiments, that the lunar rays gathered 

 to a focus produced a sensible degree of heat. Muschenbrock, however, adopts 

 the opposite opinion, and asserts that himself, De la Hire, Villct, and Tschirn- 

 hausen had tried with that view the strongest burning-glasses in vain. (Opera 

 do Ignc.) De la Lande makes a similar confession in his Astronomy (vol. ii. vii. 

 1413). Bouguer, whom we have just quoted, demonstrated that the light of 

 the moon was 300,000 degrees less than that of the sun; it would consequently 

 be necesary to invent a glass with an absorbing power 300,000 degrees greater 

 than those ordinarily in use, to try the experiment Baoou speaks of. Ed. 



