Hot and Thermal Springs, ^c. 267 



and, although it is sheltered from the direct action of the sun's 

 rays by the surrounding bushes, is yet very much more ex- 

 posed to its influence than the former spot. The place where I 

 am making the observation, mentioned in Chap. VIII., for as- 

 certaining the depth to which the influence of the external tem- 

 perature is felt, is exposed to the sun during almost the whole 

 year ; if, then, the position of a place with respect to the sun, 

 has any influence on the yearly mean, it would shew itself most 

 distinctly between this spot and that in front of the laboratory. 

 The observations which I made at the same time at these 

 two spots, extended from October 1835 to February 1836. 

 From this time till April they were unavoidably interrupted, 

 in order to sink the shaft deeper, but after April they were 

 continued. The slight difference of two feet below the surface 

 cannot have any considerable influence on the results. 



The diff'erence, therefore, at the end of October and in the 

 middle of May is ; but from the end of October till the 

 middle of IMay, tlie temperature of the place in the shade is 

 constantly higher than that of the place exposed to the sun ; 

 and from May till October it is constantly lower. Whether 

 the yearly mean temperature of the two places is the same, or 

 •whether, as we should be inclined to conclude from the above 

 observations, the mean of the place exposed to the sun is higher 

 than the other, must be decided by a series of uninterrupted 



