278 Prof. Bischof 07i the Temperature of 



No. 1 is an artificial well 58 feet deep, which, like all other 

 wells in this neighbourhood, is supplied with water from the 

 Rhine. Its high mean temperature compared with that of the six 

 following ones, is evidently caused by the increase of temperature 

 towards the interior of the earth. The mean temperatures of 

 2 — 7 agree, however, tolerably well together, and the mean of 

 these six might therefore be taken as the mean temperature of the 

 soil between Poppelsdorf and Godesherg. However I exclude 

 No. 5, because it rises from very near the surface, as is plain 

 from its more extensive variations of temperature compared 

 Avith the others, and because it evidently receives its water from 

 the neighbouring hills. In this manner, then, we obtain a 

 mean of 50°.22. The springs 8 — 18 are all situated on the 

 other side of the Rhine, in the Siebengebirge, and rise by 

 degrees above No. 1, as the annexed numbers indicate. It is 

 very remarkable that No. 8 has a mean temperature 0°.112 

 higher than No. 1, although situated considerably higher. But 

 if we examine its localities more closely, it no longer appears as- 

 tonishing ; for it rises at the foot of the Drachenfels, on the 

 eastern side, where the mountain is unusually steep ; and if it 

 runs but a few hundred feet in a horizontal direction, or at least 

 in a direction nearer to the horizontal than the slope of the 

 hill, the furthest point of its course may easily lie 100 feet be- 

 neath the surface of the mountain. It is, therefore, probable that 

 it rises from a greater depth, in comparison with the mountain, 

 than any one of the rest of the springs ; it'consequently brings a 

 higher temperature with it from the interior of the mountain, 

 and must be looked upon as thermal, although it certainly does 

 not rise from a greater depth by means of hydrostatic pressure. 

 I will pass over No. 9, because this spring runs for a consi- 

 derable distance on the surface, and I could not trace it to its 

 source. No. 10 presents a curious phenomenon, namely, when 

 I observed its temperature in December, I found, by plunging 

 the thermometer in at different parts of the little natural basin 

 which it forms, a difference of 0o.225, and remarked that there 

 are two small springs which rise here, scarcely six inches 

 apart, with different temperatures. The lower numbers shew 

 the differences of temperature between the two. I then dis- 

 covered another spring, No. 11, scarcely three paces distant 



