1848.] Observations made on a Botanical Excursion. 405 



mornings are cooler, by 1.2 degrees, the days hotter by 10°. There 

 is also 10° increase of range during the 13 days spent there; and the 

 mean range from day to day is nearly as great as it was on the hills 

 of upper Bengal. 



There being much exposed rock and the valley swept by violent dust 

 storms, the atmosphere is drier, the mean saturation point being here 

 454°, and in the lower part of the Soane's course 516°. On the other 

 hand the variation in the amount of moisture suspended in the atmo- 

 sphere is more variable than even on the hills above alluded to ; the ac- 

 cumulation of moisture in the calm nights and closer parts of the valley 

 being great ; it is rapidly swept away by the periodic dry wind of the 

 day. 



A remarkable uniformity still prevails in the depression of thermo- 

 meters exposed to nocturnal radiation, whether laid on the earth, grass, 

 or exposed to the influence of the sky alone ; both the mean and maxi- 

 mum indication coincide very nearly with those of the lower Soane valley 

 and of the hills. The temperature of tufts of green barley laid on the 

 ground is one degree higher than that of short grass as it grows ; Arge- 

 mone and Calotropis leaves maintain a still warmer temperature ; from 

 the previous experiments the Agemone appeared to be considerably the 

 cooler, which I was inclined to attribute to the smoother and more 

 shining surface of its leaf, but from these there would seem to be no 

 sensible difference between the radiating powers of the two plants. 



Here, as on the hills, there is less difference between the forenoon and 

 afternoon indication of the black-bulb thermometer, than in the more 

 open valley, which is to be accounted for by my having been obliged to 

 choose too late an hour for the forenoon observation. 



The rapid drying of the lower strata of the atmosphere during the 

 day, as indicated by the great decrease in the tension of the vapor and 

 the saturation point, from 9 a. m. to 3 p. m. is the effect of the great 

 violence of the N. W. winds. 



March 3rd. — Rode to Roump, at the top of the pass in the hills 

 called "Ek powa" (or one foot) ghat. The village of Markounda, at 

 the foot of the ghat, is situated by a stream running over flat beds of 

 limestone, fissured as to resemble a tessellated pavement ; the fissures 

 were filled apparently with volcanic matter, but the evening was too 

 fast closing in to allow of my examining it. This, the only ascent to 



3 h 2 



