266 



Prof. Bischof on the Temperature of 



We see that the maxima and minima do not happen at the 

 same time ; but that they take place later on the more elevated 

 spot, and that as the decrease of temperature varies according 

 to the seasons, so does also the decrease of tempei'ature in the 

 soil vary. The mean difference of temperature between Bonn 

 and \heL'6we7iburg gives a mean decrease of temperature of 2°.25 

 in every 683 feet between the two places. This number is so 

 nearly the same as the mean of Boussingault's observations, that 

 ■we may certainly be allowed to consider the decrease of tem- 

 perature with the height, between the tropics and in 51° N.Lat., 

 as identical, at least to the height of 1 1 73 feet. 



In these observations another circumstance must be taken in- 

 to consideration, namely, whether each two points of observa- 

 tion, at different heights, must lie in the same position with re- 

 spect to the sun ; that is to say, whether they must both lie in 

 the shade, or be exposed to the sun ; or has this no influence on 

 the yearly mean .'* The point of observation in front of my 

 laboratory lies during the whole year in the shade ; that on the 

 Lbzeenburg is in a little hollow on the top of the mountain, 



" I was prevented from observing from the 8th August till the 21st Octo- 

 ber by my journey to the Alps, and afterwards by indisposition. The obser- 

 vations on the 30ih August were made by an observer whose accuracy may 

 be depended on. However, this gap can have no perceptible influence. Nei. 

 ther can it have been prejudicial to the accuracy of the results, that the ob- 

 servations were not always made on the same day of the month, which was 

 rendered impossible by my other duties and by unfavourable weather. The 

 object of these observations was not so much to ascertain with the utmost 

 exactitude the mean temperature of the places, as to learn the mean differ- 

 ence of temperature between two places situated at dififerent heights. 



