276 Prof. Bischof on the Temperature of 



mean temperature of variable springs can only be found by 

 means of monthly observations continued for a whole year, or 

 by observing exactly at the time of their mean temperature. 

 When once the time of the maximum or minimum is known, it 

 is easy to determine the time of the mean, for this always hap- 

 pens three months after these extremes. 



But mountain springs scarcely ever give the true tempera- 

 ture of the place at which they rise, but generally of a more 

 elevated region, that is to say, they bring cold with them from 

 above.— (Chap. IV). 



From this it follows, that single observations on springs are 

 of no use for the determination of the mean temperature of the 

 soil, for repeated observations are necessary for deciding whe- 

 ther the springs have a constant temperature or not, and if not, 

 when its mean happens. But it is impossible to discover 

 whether a spring give the^true temperature of the place, with- 

 out the assistance of observations on the temperature of the 

 soil itself. Thus it follows, that even monthly observations of 

 mountain springs, continued for a whole year, cannot be of use 

 for the determination of the mean temperature of the soil. 



The following table contains the results of one year's obser- 

 vations made by me on the temperatures of eighteen springs 

 which rise between Poppelscloj^ near Bonn, and the highest 

 points in the Seven Moimta'ins {Skbengeb'u-ge), at which springs 

 are still to be met with. It proves what we have just said 

 most clearly. 



The numbers between parentheses were determined by inter- 

 polation, but all the rest by observations, made for the most 

 part in the middle of the month, excepting when other duties 

 or unfavourable weather prevented it. As the greater number 

 of these springs shewed but small variations from month to 

 month, it could be of little consequence whether the obser- 

 vations were made a few days earlier or later in the month. 

 The first seven springs rise all nearly on the same level, on the 

 slope of the hills belonging to the lignite formation, which run 

 from Poppelsdorf io Godesberg. The ground rises impercep- 

 tibly from the former of the places to the latter. 



