372 



THE POPULAR SCIENCE MONTHLY. 



Fig. 1. 



and twenty-three and a half metres (seventy-six and a half feet) deep, 

 which widens out above into a tunnel-shaped basin, B, from two to 

 three metres (six and a half to ten feet) deep, and seventeen to twenty 

 metres (fifty-five to sixty and one half feet) in horizontal extent. The 



walls of the basin are formed of a, 

 cone of siliceous sinter, S, from six 

 to nine metres (twenty to thirty 

 feet) high, and about sixty -five 

 metres (more than two hundred 

 feet) broad. The water of the gey- 

 ser is crystal-clear, with a greenish 

 tint, and flows, except immediately 

 after an eruption, steadily over the 

 rim of the basin. A double mo- 

 tion may be perceived in the col- 

 umn of water inside of the cylinder. 

 A hot stream ascends from the bot- 

 tom in the axis of the cylinder, 

 while the cooler water descends by 

 the sides, but only to about half- 

 way down, for it there unites with the rising hot current and ascends 

 again to the surface. The temperature of the water is 179 at the 

 surface of the basin ; rises at the bottom of the basin to 192, and 

 rises in the bottom of the cylinder to 251 and 260. The peculiarity 

 of the intermittent streams consists in the fact that their waters mixed 

 with steam are forcibly thrown up in huge jets at longer or shorter 

 intervals. At the Great Geyser, jets of steam, accompanied by detona- 

 tions raising the water to the height of about ten feet, appear in 

 different parts of the basin at intervals of from one and a half to two 

 hours. At intervals of from twenty-four to thirty hours, a column 

 of water, mixed with steam, rises over the whole extent of the cylinder 

 and the basin, with a sound as of distant thunder, to a height of from 

 twenty-five to thirty metres (eighty to ninety-three feet), and scatters 

 clouds of spray. After an eruption of this kind, the duration of which 

 is about ten minutes, the basin and cylinder are empty ; they are 

 gradually filled up again in the course of from four to six hours, after 

 which the processes described above are repeated. The loss of water 

 occasioned by the eruption and overflow is made up for by side- 

 streams, a part of which, W, being near the surface, probably bring in 

 cold water; others, W, entering at the bottom, water of a higher tem- 

 perature than the boiling-point. 



The following theories have been advanced in explanation of the 

 periodical eruptions of the Great Geyser, and of the phenomena of in- 

 termittent springs generally : 



According to Mackenzie's theory, a hollow space, b, Fig. 2, exists 

 in the interior of the earth wherever an intermittent spring occurs, 



