T. A. Jaggar — Conditions affecting Geyser Eruption. 325 



tion is continuous; the effective head of water at the orifice of 

 exit is fairly constant : in the case of Old Faithful the water- 

 column is in equilibrium, and replacement occurs only after 

 each eruption, when this equilibrium has been disturbed by the 

 ejection of the column. 



2. Experimental Demonstration. 



A simple device to illustrate this process was described by 

 G. Wiedemann* and mentioned by Andrese.f Wiedemann 

 made no geological comparisons, the apparatus having been 

 constructed for class-room illustration in physics ; and most of 

 the geological experi- 

 menters have used 

 back-flow apparatus, 

 without supply reser- 

 voirs. The essential 

 parts of Wiede- 

 mann's apparatus are 

 a water-column heat- 

 ed below, and a sup- 

 pi y - tube entering 

 this column and con- 

 necting it with a res- 

 ervoir of cooler, 

 superficial waters. 

 When the excess of 

 steam generated has 

 thrown out the main 

 column, cooler water 

 filters in through the 

 supply tube, and fills 

 the geyser tube to the 

 level of the reservoir. 

 For effective and reg- 

 ularly repeated gey- 

 ser eruptions, the 

 reservoir level must 

 be maintained a little 

 below the height of 

 the mouth of tbe 

 geyser tube. 



The accompanying 

 figure illustrates 

 Wiedemann's appara- 

 tus, as it has been 

 used by the writer. 

 The dimensions are 



* Wiedemann's Annalen, xv, 1882, p. 173. f •• c -> P- 4 - 



