36 SOANE VALLEY. Chap. II. 



being now satisfactorily identified with the Eranoboas of 

 the ancients.* 



The alluvium is here cut into a cliff, ten or twelve feet 

 above the bed of the river, and against it the sand is blown 

 in naked dunes. At 2 p.m., the surface-sand was heated 

 to 110° where sheltered from the wind, and 104° in the 

 open bed of the river. To compare the rapidity and depth 

 to which the heat is communicated by pure sand, and 

 by the tough alluvium, I took the temperature at some 

 inches depth in both. That the alluvium absorbs the 

 heat better, and retains it longer, would appear from the 

 following, the only observations I could make, owing to the 

 tenacity of the soil. 



2 p.m. Surface 104° 

 2J inches, 93 



.m. Surface 51° 

 28 inches, 68 & 



Sand at this depth, 78* 



Finding the fresh milky juice of Calotropis to be only 72°, 

 I was curious to ascertain at what depth this temperature 

 was to be obtained in the sand of the river-bed, where 

 the plant grew. 



Surfaco 



. 104- 



1 inch. 



. . 102 



2 „ • 



. 94 



n „ 



. . 90 



3£ inches . 85° Compact. 



8 „ . . 73 Wet. 

 15 „ . . 72 Ditto. 



The power this plant exercises of maintaining a low 

 temperature of 72°, though the main portion which is 

 subterraneous is surrounded by a soil heated to between 

 90° and 104°, is very remarkable, and no doubt proxi- 

 mately due to the rapidity of evaporation from the foliage, 



* The etymology of Eranoboas is undoubtedly Hierrinia Vahic (Sanskrit), the 

 golden-armed. Sona is also the Sanskrit for gold. The stream is celebrated 

 for its agates (Soane pebbles), which are common, but gold is not now obtained 

 from it. 



