130 CAPT. NEWBOLD ON THE TEMPERATURE OF THE SPRINGS, WELLS' 



In order to obtain a better idea of the degree of heat absorbed and given out by 

 the alluvium of the Nile, the sands and rocks in the beds of the rivers of India, I 

 made the following observations. 



In July 1840, a thermometer placed on the dark alluvium, then quite dry, of the 

 Nile opposite the pyramid of Meydtin at 12j p.m., having its bulb covered 0*1 of an 

 inch with the same alluvium, stood at 136°-5. With, and on, the sand of the desert 

 on the verge of the inundation line, at the same hour, it stood at 12l°*5. The tempe- 

 rature o/ the air at the time, five feet above the surface of the dark alluvium, was 

 105°-5 : the same height above that of the desert, it was 103°*5 ; sky unclouded. 

 Although the surface of the sands during the clear serene nights of Egypt is cooled 

 considerably by radiation, still a little below the surface they retain a great portion 

 of the solar heat. In July, at sunrise, the surface of the sandy desert, on the banks 

 of the Nile at Thebes, lat. 25° 26' N., which during the heat of the day indicated 

 a temperature of 130°, had cooled down to 69°-5, while the thermometer a foot helow 

 the surface stood at 83° : temperature of the air 7^°. 



The temperature of the granite rocks in the beds of the Toombuddra and the 

 Kistnah, during the months of May and June, at 2 p.m., I found from 118° to 120°: 

 during the night they cooled down usually to 83°. The temperature of the surface 

 sands in these rivers was slightly higher than that of the granite. 



The temperature of rivers whose supply, like those in South India, depends more 

 on the periodical rains than oh springs, is consequently influenced by the tempera- 

 ture of the former. That of the monsoon showers, which fell on the western coast 

 near Mangalore during the months of May and June, varied from 73° to 79°, afford- 

 ing a mean of 76°. The rains falling on the elevated table-land of the Ceded districts, 

 from June to December, ranged from 71°'5 to 79°'5, giving the mean 75°'5. The mean 

 general height of the plain, between lat. 13° and 17° N., is 1300 feet above the sea's 

 level. The temperature of the showers was invariably modified by the conditions 

 affecting that of rain water in extra-tropical countries, namely, the elevation at which 

 condensed, and the temperature of the atmospheric strata through which the showers 

 fell. 



The temperature of the Brahmaputra river at Sadya in Assam, was found in 

 September by Mr. Griffiths to range from 63° to 70°. That of the air above the 

 river, from 68° to 100°. That of the Indus, by Gerard, in March, near Attock, 

 was 32°. 



Temperature of the Ocean on the Equator and between the Tropics. — The influence of 

 the trade-winds, cold currents from high latitudes, frequent showers, evaporation, 

 &c., contribute to cool the air and surface of the ocean at the equator. The ex- 

 tremes of the temperature of the latter, at great distances from land, have been 

 pretty correctly stated by M. Arago at 80°' 8 and 84°'2. On crossing the line in the 

 Atlantic Ocean (in long. 20°7 W.) I found the temperature of the sea 84°'5 ; air in the 

 shade, 87° : in the Indian Ocean (long. 58°-54 E.) 81°-5 ; air in the shade 82°-5. In the 



