178 GEYSERS. 
photographs, and led to experiments by the Geological Survey* show- 
ing that eruptions can be produced in many cases of geysers, which have 
been most capricious in their exhibitions, or have been inactive for 
weeks or even months. The conditions essential to the successful use 
of soap or lye for this purpose seem to be that the geyser tube be small, 
and the water near its boiling point, if not actually boiling at the sur- 
face. Many of the bowls in the Yellowstone possess a temperature at 
their surface exceeding the theoretical boiling point for the altitude 
by lor 2 degrees. This apparently anomalous fact is not due to the 
mineral matter held in solution by the hot waters, for the analyses 
show that amount to be too small to have any appreciable effect, but 
it is explained by the waters being free from air, it being well known 
to physicists that water freed from air has an increased boiling point, 
because of the greater cohesion of the particles. The effect of the 
soap is to increase the viscosity of the water, the consequent explosive 
liberation of steam producing an eruption. 
Variations in geyser periods—Many geysers are easily mistaken for 
simple hot or boiling springs, since during the long intervals between 
eruptions they present no indications of their true nature. 
The interval between eruptions is manifestly dependent upon the two 
factors of heat and water supply. It rarely happens that these fac- 
tors are so constant that the geyser has a definite period. Even in the 
‘vase of Old Faithful, tie most reliable of all geysers, there are very 
considerable variaticns in the period, though the average is always con- 
stant from day to day. 
It sometimes happens that a slight change in the conditions—a les- 
sened amount of heat or increased amount of water—will cause a ces- 
sation of a geyser’s eruptions for a long period. This has happened in 
New Zealand, where the Waikite geyser, near Lake Rotorua, inactive 
for many years, suddenly exploded, scattering blocks of sinter and 
scalding several Maoris who happened to be near by. The Excelsior, 
undoubtedly the largest geyser of the world, was not seen in action 
until 1878, continuing its periodic eruptions till 1882, when it ceased 
and did not play again until1888. Last summer it was again inactive, 
though the water boiled furiously, bulging up several feet in the center 
of the great caldron. 
Observations made in New Zealand have led to the belief that the 
eruptions of certain geysers were influenced by the barometric pres- 
sure, and itis said that certain geysers are only active during the prev- 
alence of a northwest wind. Observations in the Yellowstone show no 
such correspondence. Asa rule the water surface exposed is small and 
the effect of temperature and pressure would be scarcely appreciable, 
yet theoretically it is quite probable that when the forces in a geyser 
are in a delicate equilibriuin a change of temperature and pressure of 
the air would be quite sufficient to cause an eruption. 
* ““Soaping Geysers,” Arnold Hague. [Trans. Am, Inst, Min. Eng., Feb., 1889.] 
