1840,] 



afid Mountains of N. W, India, 



U5 



Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dee. 



Maximum.... 84-5 85 87 87 89 88 88 88 88 88 86 86 

 Minimum.... 70-5 73 73 74 75 74 74 75 75 75 74 74 



77-5 79-5 80 80-5 83 81 81.5 81-5 81-5 81-5 80 80=80-4 

 This degree of equability is found near the Equator only, but an ap- 

 proach is made to it during the rainy season of the year, both in higher 

 latitudes and at considerable elevations, within the influence of the tro- 

 pical rains, though the general characteristics of these situations is that 

 of variableness of climate, or of a great range of the thermometer, both 

 daily and annual. The result is the production, not only of great cold, 

 but also of great heat, so that the thermometer is found to rise much 

 higher at, and a little beyond the tropics, than in the neighbourhood of 

 the Equator. This is accounted for, in some measure, by what has been 

 observed by astronomers, that the sun, in his progress from the Equator 

 towards the Tropic, advances in the first month 12°, and in the second 

 8°, so that at the end of the second month he is 20° from the Equator, 

 and takes a month to advance the remaining 3^'', and an equal time to 

 return, so that during the whole of this period the solar rays must fall 

 nearly perpendicularly at noon on all places between 20*^ and 23 J" of 

 latitude, while a place situated under the Equator has the sun only 

 during six days, as near the zenith, as the above places near the tropics 

 have it for near two months ; and, therefore, we may expect a greater 

 degree of heat, which is moreover increased by the greater length of 

 the days. The larger proportion of land near and beyond the tropic of 

 Cancer, as well as the sandy barren nature of the soil, perhaps origi- 

 nally a consequence of, but now acting as a cause, in increasing the 

 heat, together with the dryness of the air, all contribute, as causes, in 

 increasing the absorption of, and the subsequent radiation of the heat 

 imparted by, the nearly perpendicular solar rays. Thus Ritchie and 

 Lyon state, that during whole months the thermometer stood at 117**, 

 and at 128' in the Oasis of Mourzouk; Dr. Coulter mentions having 

 observed it at 140° on the banks of the Rio Colorado, 32' 30' N. lat., 

 and we have it often stated as being 120°. Mr. Everest gives 111° as 

 the highest at Ghazeepore; Mr. Prinsep as its being 114° at Benares. 

 1 have observed it at 107° at Saharunpore. The free radiation of the 

 same open plains in the clear still nights of the winter months, causes 

 a degree of cold which one is surprised to hear of as occurring in situa- 

 tions where the summer heat is so intense ; hence the coldness experi- 

 enced in some of the deserts of Africa, also by Lieut. Burnes, as well 

 as in the plains of India. 



