}■ 



186 On Solar Radiation. 



raised the blackened thermometer above one in the shade 

 as follows : — 



At Rio Janeiro, Lat. 12' 47 e 



London, Lat. 69° 69° J- o heit. 



Arctic Regions, Lat. 90° 



From this he drew the following conclusion: " That the 

 force of solar radiation increases from the Equator to the 

 Poles." For this inference, which he had supported by many 

 experiments, Daniel has been severely censured by some 

 of the continental physicians, and accused of advancing his 

 remarks with confidence and presumption. 



The inference from Scoresby's observations does not ap- 

 pear to have been warranted, from the last observations 

 made with proper instruments by Franklin, Back, and 

 Richardson in the Arctic circle, who have shewn that the 

 maximum radiating power is not more than 53.° It is possi- 

 ble some contingent circumstances, such as evaporation or 

 proximity to a surface of snow may have affected these 

 results ; but, however, that may be true or not, yet Scoresby's 

 observation stands as an incontestable fact. He remarks that 

 when in the Arctic regions, he saw the pitch melted out 

 of the seams of a ship by the heating power of the sun's 

 rays impinging on the black exterior, when on the opposite 

 side, in the shade, the temperature was 20° of Farhenheit. 

 As Daniel found pitch to melt imperfectly at 136°, he there- 

 fore estimated the solar radiation at about 90°. When it is 

 remembered that in India the utmost power of the sun's rays 

 can hardly melt the pitch off a gun or a tarpaulin, and 

 only slightly off the new tarred rigging of a ship, even when 

 the temperature of the air is 90', there is strong evidence 

 for supposing that the sun has a greater heating power near 

 the Poles than near the Equator. 



The correctness of Captain Sabine's experiments has been 

 questioned, because he laid the blackened thermometer ex- 

 posed to the sun's rays on some dry plants, raised only a few 



