GEOLOGY. 271 



they are situated within 40 miles of those cones and lava-streams of the 

 Eifel, which, though they may have spent their force ages before the 

 earliest records of history, belong, nevertheless, to the most modern ge- 

 ological period. Bath is about 400 miles distant from the same part of 

 Germany, and 440 from Auvergne, another volcanic region, the latest 

 eruptions of which were geologically coeval with those of the Eifel. I 

 have little doubt that the Bath springs, like most other thermal waters, 

 mark the site of some great convulsion and fracture which took place in 

 the crust of the earth at some former period, perhaps not a very remote 

 one, geologically speaking. 



Mineral Constituents of Hot Springs. If we adopt the theory 

 already alluded to, that the nitrogen is derived from the deoyxdation 

 of atmospheric air carried down by rain-water, we may imagine the 

 supply of this water to be furnished by some mountainous region, 

 possibly a distant one, and that it descends through rents or porous 

 rocks till it encounters some mass of heated matter by which it is con- 

 verted into steam, and then driven upwards through a fissure. In its 

 downward passage the water may derive its sulphate of lime, chloride 

 of calcium, and other substances from the decomposition of the gyp- 

 seous, saline, calcareous, and other constituents of the rocks which it 

 permeates. The greater part of the ingredients are common to sea- 

 water, and might suggest the theory of a marine origin ; but the analy- 

 sis of the Bath springs by Merck and Galloway shows that the relative 

 proportion of the solid matter is far from agreeing with that of the 

 sea, the chloride of magnesium being absolutely in excess, that is, 14 

 grains of it per gallon for 12 of common salt ; whereas in sea-water 

 there are 27 grains of salt, or chloride of sodium, to four of the chlo- 

 ride of magnesium. That some mineral springs, however, may 

 derive an inexhaustible supply, through rents and porous rocks, from 

 the leaky bed of the ocean, is by no means an unreasonable theory, 

 especially if we believe that the contiguity of nearly all the active 

 volcanoes to the sea is connected with the access of salt water to the 

 subterranean foci of volcanic heat. 



Prof. Roscoe, of Manchester, has been lately engaged in making a 

 careful analysis of the Bath waters, and has discovered in them three 

 metals which they were not previously known to contain, namely, cop- 

 per, strontium, and lithium ; but he has searched in vain for cesium and 

 rubidium, those new metals, the existence of which has been revealed to 

 us in the course of the last few years by what is called spectrum analy- 

 sis. By this new method the presence of infinitesimal quantities, 

 such as would have wholly escaped detection by ordinary tests, is 

 made known to the eye by the agency of light. 



Prof. Bunsen, of Heidelberg, led the way, in 1860, in the appli- 

 cation of this new test to the hot waters of Baden-Baden and of Dlirk- 

 heim in the Palatinate. He observed in the spectrum some colored 

 lines of which he could not interpret the meaning, and had deter- 

 mined not to rest till he had found out what they meant. This was 

 no easy task, for it was necessary to evaporate 50 tons of water to 

 obtain 200 grains of what proved to be two new metals. Taken al- 

 together, their proportion to the water was only as one to three mil- 

 lion. He named the first caesium, from the bluish-gray lines which it 

 presented in the spectrum ; and the second rubidium, from its two red 



