460 KOVUM ORGANUM. [LOOK IL 



The reflection of the solar rays in the polar regions is found to 

 be weak and inefficient in producing heat, so that the Dutch, who 

 wintered in Nova Zembla, and expected that their vessel would 

 be freed about the beginning oi July from the obstruction of the 

 mass of ice which had blocked it up, were disappointed and 

 obliged to embark in their boat. Hence the direct rays of the 

 sun appear to have but little power even on the plain, and when 

 reflected, unless they are multiplied and condensed, which takes 

 place when the sun tends more to the perpendicular; for, then, 

 the incidence of the rays occurs at more acute angles, so that the 

 reflected rays are nearer to each other, whilst, on the contrary, 

 when the sun is in a very oblique position, the angles of incidence 

 are very obtuse, and the reflected rays at a greater distance. 1 1 

 the mean time it must be observed, that there may be many 

 operations of the solar rays, relating, too, to the nature of heal, 

 which are not proportioned to our touch, so that, with regard t) 

 us, they do not tend to produce warmth, but, with regard t&amp;gt; 

 some otSer bodies, have their due effect in producing it. 



Let the following experiment be made. Take a lens the re 

 verse of a burning glass, and place it between the hand and th ) 

 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 eithe* 

 more diffused or contracted. It should be seen, therefore, if tho 

 same be true with regard to heat. 



Let the experiment be well tried, whether the lunar rays cat 

 be received and collected by the strongest and best burninfc 

 glasses, so as to produce even the least degree of heat.* But i 

 that degree be, perhaps, so subtile and weak, as net to be per 

 ceived or ascertained by th? touch, we must have recourse tc 

 those glasses which indicate tho warm or cold state of the atmos 

 phere, and let the lunar rays fall through the burning glass on 



ascended the Andes to discover the globular form of the earth, and pub 

 lished an account of his passage, which verifies tho statement oi Bacon, 

 i Mont-uiari 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 sersiole degree oi heat. 

 Muschenbrock, however, adopts the opposite opinion, and asserts that 

 himself, De la Hire, Villet, and Tschirnhausen had tried with that view 

 the strongest burning-glasses in vain. (Opera de Igne.) De la Land 

 makesa similar confession in his Astronomy (vol. ii. vii. 1413). Bouguer, 

 \\hom we have just quoted, demonstrated that the light of the moon WOP 

 800,000 degrees less than that oi the sun : it would consequently be 

 necessary to invent a glass with an absorbing power 300,000 degrees 

 greater than those ordinarily in use, to try the experiment 

 speaks o. d. 



