THERMAL SPRINGS. 205 



mann distinguishes : 1. Purely meteorological springs, the 

 average temperature of which is not increased by the internal 

 heat of the earth ; 2. Meteorologico-geological springs, which, 

 being independent of the distribution of rain, and warmer 

 than the air, only undergo such alterations of temperature as 

 are communicated to them by the soil through which they 

 flow out ; 3. Abnormally cold springs, which bring down 

 their coldness from great elevations. 80 The more we have 



60 " In order to ascertain the amount of variation of the average tem- 

 perature of springs from that of the air, Dr. Ecluard Hallmann observed 

 at his former residence, Marienberg, near Boppard, on the Rhine, the 

 temperature of the air, the amount of rain and the temperature of seven 

 springs for five years, from the 1st December, 1845, to the 30th No- 

 vember, 1850 ; upon these observations he has founded a new elabora- 

 tion of the relative temperature of springs. In this investigation the 

 springs with a perfectly constant temperature (the purely geological 

 springs) are excluded. On the other hand, all those springs have been 

 made the subject of investigation which undergo an alteration in their 

 temperature according to the seasons. 



" The variable springs fall into two natural groups : 



" 1. Purely meteorological springs : that is to say, those whose ave- 

 rage is demonstrably not elevated by the heat of the earth. In these 

 springs the amount of variation of the average from the aerial average is 

 dependent upon the distribution of the animal amount of rain through 

 the 12 months. These springs are on the average colder than the air 

 when the proportion of rain for the four cold months, from December 

 to March, amounts to more than 33^ per cent.; they are on the average 

 warmer than the air, when the proportion of rain for the four warm 

 months, from July to October, amounts to more than 33 per cent. 

 The negative or positive difference of the spring-average from the air- 

 average, is larger in proportion to the excess of rain in the above-men- 

 tioned cold or warm thirds of the year. Those springs in which the 

 difference of the average from that of the air is in accordance with 

 the law, that is to say, the largest possible by reason of the distribution 

 of rain in the year, are called purely meteorological springs of undis- 

 torted average ; but those in which the amount of difference of the 

 average from the air average is diminished by the disturbing action of the 

 atmospheric heat during the seasons which are free from rain are called 

 purely meteorological springs of approximate average. The approxima- 

 tion of the average to the aerial average is caused either by the enclo- 

 sure, especially by a channel at the lower extremity of which the tem- 

 perature of the spring was observed, or it is the consequence of a super- 

 ficial course and the poverty of the feeders of the spring. In each year 

 the amount of difference of the average from the aerial average is 

 similar in all purely meteorological springs, but it is smaller in tho 

 approximate than in the undistorted springs, and indeed is smaller in 

 proportion as the disturbing action of the atmospheric heat is greater 



