264 Prof. Bischof 07i the Temperature of 



responding so nearly seems rather to lead to the conclusion, 

 that between the tropics the decrease of temperature in the air 

 and in the soil follow the same law of progression. 



For the reasons above giren, the decrease of temperature in 

 the air in the temperate^zones can only be deduced from the 

 known mean temperatures at different heights. Here, then, we 

 are confined to the habitable regions. All that we as yet know 

 of the decrease of the temperature of the air in the temperate 

 zones is from the corresponding observations made during se- 

 veral years at Geneva and on the St Bernhard. The mean 

 of these observations gives a difference of 777.5 feet for every 

 degree of Reaumur, or 2°25 degrees of Fahrenheit. This re- 

 sult exceeds the mean of Humboldt's observations by 123 feet, 

 and that taken from Boussingault's by 100 feet ; but it is far 

 lower than the former of these philosophers found for moun- 

 tains having a very gradual ascent. But as St Bernhard is 24 

 leagues distant in a straight line from Geneva, and the differ- 

 ence of height between the two places is only 6477 feet, it may 

 be considered as being a case of gradual ascent ; and the tem- 

 perature must decrease less rapidly than if the mountain had a 

 steep precipitous ascent. To conclude that the decrease of 

 temperature in the temperate zones is less rapid than between 

 the tropics, would, therefore, certainly be premature. 



The first question to be decided is, whether, in the temper- 

 ate zones, as between the tropics, the mean temperature of the 

 soil and of the air are identical, in elevated situations, as well as 

 on the level of the sea. If this be found to be the case, we may, 

 instead of the tedious observations in thfe air, which at uninha- 

 bitable heights are, indeed, quite impracticable, substitute ob- 

 servations in the soil, which, although also combined with diffi- 

 culties, are yet possible to be accomplished. But this question 

 can be most easily answered by the observations at the Monas- 

 tery of St Bernhard, where the mean^temperature of the air is 

 known, and where meteorological observations continue to be 

 made. 



The simplest method of obtaining the temperature of the 

 soil, as I have found, is, to dig a hole about four feet deep, and 

 to sink a wooden case of the same depth into it, and then to fill 

 up the surrounding space with earth or sand. The case should 



