392 Observations made on a Botanical Excursion. [Oct. 



there recorded) amounting to 17.2 in the former and only 12°8 in the 

 lower station. The range from the maximum to the minimum of each 

 day amounts to the same in both, above 20°. The extreme variations 

 in temperature too coincide within 1°4. 



In the hygrometric state of the atmosphere, this of the plains 

 differs most decidedly from that of the hills. Here, as I remarked, 

 dew is constantly formed, which is owing to the amount of moisture in 

 the air, for nocturnal radiation is more powerful on the hills, though it 

 never caused a thermometer to descend to the dew point there. The 

 sunrise and 9 p.m. observation on the lower level give a mean depres- 

 sion of the D. P. below the air of 12°. 3, and those at the upper level of 

 21°. 2, with no dew in the former case and a copious deposit in the latter. 

 The corresponding state of the atmosphere as to saturation is 0.480 on 

 the hills and 0.626 below. The only causes I can assign for this seem 

 hardly sufficient : they are the more uniform depth and presence of the 

 alluvium and the frequency of rivers ; and what perhaps is even 

 more powerful the shelter afforded by the Kymaon hills from the dry 

 N. W. winds ; though it is difficult to conceive that hills of only 1000 

 feet elevation can influence much a valley 80 miles broad (between the 

 Kymaon and Dunwah.) 



The vegetation of the Soane valley is exposed to less extremes of 

 temperature, than that of the hills. The difference between solar and 

 nocturnal radiation amounting here only to 80°. 5, and in the former 

 case to 9 6°. 5. There is no material difference in the power of the sun's 

 rays at the upper and lower level, as expressed by the black bulb 

 thermometer, the average rise of a thermometer so exposed over one 

 in the shade, amounting to 48° in either case, and the maximum occur- 

 ring about 11 a. m. The decrease of the power of the sun's rays in 

 the afternoon is much the most rapid in the valley, coinciding with a 

 greater reduction of the elasticity of vapor and of humidity in the 

 atmosphere. 



The photometric experiments show a greater degree of sun's light on 

 the hills than below, but there is not in either state a decided relation 

 between the indications of this instrument and the black bulb thermo- 

 meter. From observations taken elsewhere I am inclined to attribute 

 the excess of solar light on the hills to their elevation ; for at a far 

 greater elevation I have met with much stronger solar light, in a very 



