J. C. Graham — Experiments with an Artificial Geyser. 55 



increase of heat causes an expansion of mercury in the bulb below, 

 thereby decreasing the heat by cutting off the gas. The ob- 

 ject of this device is to maintain, as nearly as practicable, a 

 constant temperature in the mercury. The whole is supported 

 upon a frame not shown in the figure. 



The important dimensions of the apparatus are : 



Internal diameter of inner cylinder 0*089 m 



" height " " 0-136 m 



" diameter of tube 0-02 l m 



.Height of tube 1 '44 m 



Height to which cone is filled 0-035 m 



Total height of fluid column 1-61 l m 



With this apparatus we are enabled to get not only qualita- 

 tive but quantitative results to a large extent, for all the factors 

 are nearly constant, and where variable, the amount of varia- 

 tion can be detected. 



The object of my experiment was to see if any light could 

 be thrown upon the subject of " soaping geysers " by the 

 study of an artificial one. But before considering this subject, 

 I wish to mention an observation which seems to me to give a 

 criterion, judged by which certain geysers can be proven not 

 to operate upon the McKenzie principle. 



It will be recalled that Sir George in explaining the phe- 

 nomenon of an eruption supposed a tube communicating with 

 a subterranean cavern in the way indicated in the accompany- 

 ing sketch, fig. 2. 



The water is kept in the tube at the level indicated, by the 

 steam pressure in A, arising from the heated water B. An 

 eruption takes place when the pressure in the cavity becomes 

 great enough to lift the column in the tube sufficiently to 

 cause an overflow and thus to lessen the pressure of the col- 

 umn. By forcing the tube of my artificial geyser part way 



