280 Prof. Bischof on the Temperature of 



differs by 0°.787 from the above-mentioned mean obtained from 

 the direct observations on the temperature of the soil ; but, as 

 the observations on the springs occupied the space of time from 

 August 1834 to August 1835, and therefore included the mild 

 winter of 1834-35, whilst the observations in the soil lasted 

 from February 1835 to February 1836, and included the severe 

 winter of 1835-36, we cannot be surprised at this difference. 

 And, in fact, the observations on the temperature of the soil 

 shew a considerable fall from October 1835 to February 18S6.* 

 My observations communicated in Chap. VIII., so far as they 

 can be reckoned upon, are also in unison with this. But the 

 necessity of observing the rule, already laid down in Chap. VI., 

 never to attempt to determine the mean temperature of a place 

 but from several springs, is rendered obvious by comparing 

 the spring No. 1 with the six following ones. The less the 

 extent of the variations of temperature in a spring is, the more 

 probable is it that it brings up heat with it from below ; and, 

 indeed, we find the extent of variation in Nos. 1-7 to decrease 

 in proportion as the mean temperature increases. 



For the reasons explained in Chap. VIII., it may with pro- 

 bability be assumed that the springs Nos. 5, 7, and 17 rise 

 from a depth of about twenty-four feet, but the rest from 

 a greater depth. Nos. 8, 10, 12, and 13, rise without doubt 

 from the greatest depth, which may easily amount to 60 feet, 

 when we compare their scales of variation with that of No. 1. 

 The comparatively high temperatures of Nos. 8 and 12, of 

 which we have already before made mention, are easily ac- 

 counted for, when we consider that they rise in deep ravines, 

 so that the rocks rise steeply and to a considerable height on 

 both sides. If these do actually rise from a depth of sixty feet, 

 they may very easily acquire a mean temperature of 1°.125 

 higher than that of the surface, by reason of the increase of 

 temperature towards the interior of the earth. 



If the depth from which springs rise could be ascertained, 



• The mean temperature of the air at Bonn is not yet accurately deter- 

 mined. But the mean of the Medical assessor Mohr's fourteen years' obser- 

 vations at Coblentz, from 1818 to 1831, corrected according to the rule in 

 Baumgartner's Naturlehre, 3d edit. p. 697, is 5r.l2. 



