Sot Springs, and other Natural Features of the Pyrenees. 445 



not large But deep, rises to the surface through a natural 

 chasm in the rock. The water is conducted to the establish- 

 ment, near the spring, with the least possible loss of tempera- 

 ture, by subterranean tubes. At the " Source de Plnterieur" 

 the buvette is not more than a yard from the actual source, 

 which is an oval recess, excavated to a depth of three feet 

 in the rock. The normal condition of this spring, like 

 the rest of those at Bagneres de Bigorre, is saline, but at 

 irregular intervals it becomes sulphurous. The volume of the 

 water at the same time enlarges. It is supposed, in explana- 

 tion of this property, that water of infiltration from the surface 

 soil, carrying with it organic matter, enters the spring, and, 

 aided by heat, effects the decomposition of sulphate of lime 

 and other mineral sulphates in the water, from which sulphu- 

 retted hydrogen is evolved. Alkaline sulphides, particularly 

 sulphuret of calcium, occur among the forms in which sulphur 

 is found in the Pyrenean springs. 



At Eaux Bonnes, and at Eaux Ohaudes, some interesting 

 traces of variation are found in the observations of Professor 

 Forbes and Dr. Scoresby Jackson. The notes of other 

 observers tend to show, however, that these changes are not 

 permanent, the temperatures of these springs having fluctuated 

 several times during the short interval of thirty years, to the 

 extent of two or more degrees. A hot spring, employed at 

 Ax as a street fountain, has, moreover, preserved its high 

 temperature, with only a small range from 166° to 169° Fah- 

 renheit, unchanged for eighty years. 



M. Filhol, the Head of the College of Medicine at 

 Toulouse, who has devoted much of his personal attention to 

 the subject, believes that, in general, springs of a high 

 temperature are less susceptible of variations than those of a 

 low temperature. This might naturally be expected to occur 

 from the fact that the hottest springs have probably also the 

 deepest source ; the cooler springs, rising probably from a 

 smaller profundity, and belonging to more permeable strata, 

 are more exposed on this account to infiltration. In this group 

 of variable springs, M. Filhol has observed that, with a 

 change of temperature, there is generally a corresponding- 

 change in the volume of the water, a lower temperature being 

 observed with an increase in the abundance of water. Never- 

 theless, M. Filhol has found that the temperatures of springs 

 — even those best regulated, and most protected from water 

 of infiltration — is not absolutely invariable. A diminution of 

 temperature is sometimes observed with a diminution in the 

 volume of the water. 



Dr. Scoresby Jackson carries his conclusions further. 

 He admits that there is perhaps, in no instance, an undevi- 



