108 



IGNEOUS AGENCIES. 



Pressure in 

 Atmospheres. 



Boiling-Point. 



1 Atmos. 



2 



3 " 



4 



212° 

 250° 



2*75° 

 293° 



tion does not deposit on cooling, but only by drying. This would make 

 the building-up of a geyser-tube an inconceivably slow process, and the 

 time proportionally long. 6. The temperature of the water in the basin 

 was found to be usually 170° to 180°, and that in the tube to increase 

 rapidly, though not regularly, with depth. Moreover, the temperature, 

 both at the surface and at all depths, increased regularly as the time of 

 eruption approached. Just before the eruption it was, at the depth of 

 about forty-five feet, very near the boiling-point for that depth. 



Theory of Geyser-Eruption— Principles.— 1. It is well known that 

 the boiling-point of water rises as the pressure increases. This is shown 



in the adjoining table. 2. It follows from the 

 above that if water be under strong pressure, 

 and at high temperature, though below its 

 boiling-point for that pressure, and the press- 

 ure be diminished sufficiently, it will immedi- 

 ately flash into steam. 3. Water heated be- 

 neath, if the circulation be unimpeded, is very 

 nearly the same temperature, throughout. That it is never the same 

 temperature precisely is shown by the circulation itself, which is caused 

 by difference of temperature, producing difference in density. The 

 phenomenon of simmering is also a well-known evidence of this differ- 

 ence of temperature, since it is produced by the collapse of steam-bub- 

 bles rising into the cooler water above. 4. But if the circulation be 

 impeded, as when the water is contained in long, narrow, irregular 

 tubes, and heated with great rapidity, the temperature may be greater 

 below than above to any extent, and 

 the boiling-point may be reached in 

 the lower part of the tube, while it is 

 far from this point in the upper part. 

 Application to Geysers, — We will 

 suppose a geyser to have a simple but 

 irregular tube, without a cave, heated 

 below by volcanic fires, or by still hot 

 volcanic ejections. Now, we have al- 

 ready seen that the temperature of the 

 water in the tube increases rapidly with 

 the depth, but is, at every depth to 

 which observation extends, short of the 

 boiling - point for that depth. Let 

 absciss a d (Fig. 92) represent depth 

 in the tube, and also pressures ; and the corresponding temperature be 

 measured on the ordinate a n. If, then, a b, b c, c d, represent equal 

 depths of thirty-three or more feet, which is equal to one atmospheric 

 pressure, the curve ef passing through 212°, 250°, 275°, and 293°, at the 



1 Atmos. 



2 Atmos. 

 33-3 ft. 



3 Atmos. 

 66 "6 ft. 



4 Atmos. 

 100 ft. 



28 















/ 



■ 



/ 



/ 



/ 



/ 



y 



a 

 b 







/ 



/ 



/ 



/ 

















1 



•1 





















c7 



f3 



Fig. 92. 



