126 CAFf. NEWBOLD ON THE TEMPERATURE OF THE SPRINGS, WELLS 



superfluous in a paper limited almost to the subject of intertropical tempera- 

 ture. 



In the columns of the registers, the latitude and longitude, the approximate height 

 above the sea, the nature of the surrounding formation, the depth to the surface of 

 the water and depth of water, the temperature of the air, the month during which 

 each observation was taken, and the approximate annual mean of the climate in 

 which the wells, &c. occur, are specified as far as practicable. In the column of re- 

 marks will be found a few observations on the chemical nature of the water, and on 

 the size of the wells and springs*. Those were selected which contained water all 

 the year round ; though all were, more or less, subject to fluctuation during the wet 

 and dry seasons. The wells in Egypt differ from the " bouries" of India in being 

 less open and exposed to atmospheric influence. Those in the valley of the Nile are 

 mere shafts sunk through the black alluvium to an impervious marly and sandy bed, 

 to depths varying, according to the distance from the river, from ten to forty feet. 

 Their circumferences, like those of the Indian " pot wells," are from nine to twelve 

 yards. They mainly depend on the river for water, which is supplied by infiltration 

 through the soil, — a circumstance to be taken into consideration in all indications 

 afforded of their temperature. The wells in the deserts of Egypt, like those of Ajmir 

 and the western deserts of India, are frequently of great depth, lying under strata 

 of sand, gravel, and a calcareous sandstone, on an argillaceous or marly bed, some- 

 times at a depth of 300 feet below the surface of the surrounding country. In the 

 granitic districts of Upper Egypt, in the Thebaid desert, however, I have observed 

 springs rising through the almost vertical strata to the surface. 



In India, most of the wells marked as occurring in granite, trap, limestone and 

 sandstone, result from springs, and are consequently not so much influenced in tem- 

 perature by the monsoon rains as those in lateritic rocks, which, from their porous 

 structure, admit of the percolation of rain water to a considerable extent. 



The temperature was generally taken at about 10 a.m., a time when I found it to 

 approximate nearest the diurnal mean ; and, whenever practicable, at the depth of 

 about ten feet from the surface. 



The following are the general results of many hundred observations : — 



1st. In low latitudes the temperature of the deepest wells and springs is a little 

 higher than the mean temperature of the air. Exceptions occur : for example, the 

 temperature of a deep well at Gadigandr, on the banks of the Toombuddra, between 

 the 15th and 16th parallels of north latitude, at an elevation of about 1200 feet from 

 the sea, was so low as 72°*5 (the temperature of the air in the shade, at the time of 

 observation, 80°*5), while that of the springs and river in the vicinity was from 77° to 

 79°'5. Ranges of hills, attaining an altitude of 1500 feet above the plain, rose at no 

 great distance ; a circumstance suggesting the probability that the cold spring had its 



* The observations of others will be denoted in the column of remarks by the names of the observers. The 

 scale throughout is that of Faheenheit. 



