460 NOVUM OrtGANUM. [bOOK 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 

 V iutered in Nova Zembla, and expected that their vessel would 

 be freed about the beginning of 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 Avhen 

 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 tho 

 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 A'ery obtuse, and the reflected rays at a greater distance. In 

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

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

 which are not proportioned 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 efi'ect 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 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 difl'iised 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 pioduce even the least degree of heat.' But if 

 that degree be, perb:;ps, so subtile and weak, as not to be per- 

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

 those glasses which indicate the 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 the statement oi' Bacon. 

 1 Monl-^nari asserts in his book against the astrologers that he had 

 satisfied himself by numerous and oft-repeated operiments, that the 

 lunar rays gathered to a focus produced a sersiole degree of 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 Lande 

 makes a similar confession inhis Astronomy (vol. ii. vii. § 1413). Bouguer, 

 N\hom we have just quoted, demonstrated that the light of the moon w?uc 

 3^0,000 degi-ees less than that oi the sun : it would consequently b€ 

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

 greater than those ordinarily iQ use, to try the experim«?nt lJ««oa 

 •peaks Ot, £d. 



