41 6 



THE POPULAR SCIENCE MONTHLY. 



necessary 



condition should exist in all geysers ; neither is it at all 

 in order to explain the phenomenon of an eruption. 



To prove beyond question the truth of his theory, Bun- 

 sen constructed an artificial geyser. The apparatus (Fig. 

 10) consisted of a tube of tinned sheet-iron about ten feet 

 long, expanded into a dish above for catching the erupted 

 water. It may or may not be expanded below for the con- 

 venience of heating. It was heated, also, a little below the 

 middle, by an encircling charcoal chauffer, to represent 

 the point of nearest approach to the boiling-point in the 

 geyser-tube. When this apparatus was heated at the two 

 points, as shown in the figure, the phenomena of geyser- 

 eruption were completely reproduced ; first, the violent 

 explosive simmering, then the overflow, then the eruption, 

 and then the state of quiescence. In Bunsen's experiment, 

 the eruptions occurred about every thirty minutes. 



According to Bunsen, a geyser does not find a cave, or 

 even a perpendicular tube, ready made, but, like volcanoes, 

 makes its own tube. Fig. 1 1 is an ideal section of a geyser- 

 mound, showing the manner in which, according to this 

 view, it is formed. The irregular line, b a c, is the original 

 surface, and a the position of a hot spring. If the spring 

 be not alkaline, it will remain an ordinary hot spring ; but, 

 if it be alkaline, it will hold silica in solution, and the silica 

 will be deposited about the spring. Thus the mound and 

 tube are gradually built up. For a long time the spring 



will not be eruptive, for the circulation will maintain a fig. io. Aim- 

 nearly equal temperature in every part of the tube ricIAL Geyser. 



it may be a boiling, but not 

 an eruptive spring. But, as 

 the tube becomes longer, and 

 the circulation more and more 

 impeded, the difference of 

 temperature between the up- 

 per and lower parts of the 

 tube becomes greater and 

 greater, until, finally, the 

 boiling-point is reached be- 

 low, while the water above 

 is comparatively cool. Then 

 the eruption commences. Fi- 

 nally, from the gradual failure of the subterranean heat, or from the 

 increasing length of the tube repressing the formation of steam, the 

 eruptions gradually cease. Bunsen found geysers in every stage of 

 development some playful springs without tubes ; some with short 

 tubes, not yet eruptive; some with long tubes, violently eruptive; 



Fig. 



11. Ideal Section of a Geyser-Tube 

 (according to Bunsen). 



