NOVUM ORGANUM 377 



sacrifices on the altar of Jupiter, by the fingers of those who had 

 offered them, would remain undisturbed till the next year. 

 Those even, who at this day go to the top of the Peak of Tene- 

 riffe, walk by night and not in the day-time, and are advised and 

 pressed by their guides, as soon as the sun rises, to make haste 

 in their descent, on account of the danger (apparently arising 

 from the rarity of the atmosphere), lest their breathing should 

 be relaxed and suffocated. 



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 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 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 con- 

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

 incidence are very obtuse, and the reflected rays at a greater dis- 

 tance. 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 re- 

 gard to us, they do not tend to produce warmth, but, with re- 

 gard to some other 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 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 un- 

 equal 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. But if 

 that degree be, perhaps, so subtile and weak, as not to be per- 

 ceived or ascertained by the 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 

 the top of this thermometer, and then notice if the water be de- 

 pressed by the heat. 



Let the burning glass be tried on warm objects which emit no 

 luminous rays, as heated but not ignited iron or stone, or hot 

 water, or the like; and observe whether the heat become in- 

 creased and condensed, as happens with the solar rays. 



