on the principal Geysirs of Iceland. 



407 



the bottom. The level of the water, which generally stands 

 at rather above three metres below the ground, falls prin- 

 cipally after great eruptions, but it sometimes rises suddenly ; 

 and the surface of the water is incessantly boiling. 



The following are some observations I made upon these 

 oscillations : — 



8th July, at 4^ 30"^ p.m. : depth below the surface . 3*40 

 9lh July, at 1 1 o'clock a.m. : after a great eruption . 4"22 

 9th July, after a second eruption, immediately after 



the first 4'55 



9th July, at 3 o'clock p.m. : Strokkur calm ; depth . 3"35 

 9th July, at '^^ 15"^ p.m. : after a great eruption . . 

 9th July, at '^'^ 59"^ p.m. : Strokkur calm .... 



9th July, at 5^ 32'^ p.m. -.Id 



9th July, at T'^ 15"" p.m. : 7rf 



10th July, at 6ii 57°i p.m.: /c? 



To determine the temperature of this column of water, we 

 employed the same thermometers as at the Great Geysir; 

 but we only arranged three on a line. The following are the 

 results obtained in these three experiments : — 



4-40 

 4-40 

 3-05 

 3-50 

 3-55 



Third Experiment. 



10th July, at d^ 57" p.m., six hours after a great eruption ; 



height of the column of water above the bottom, 10 metres. 



Heights. 



in 



y'!)-9 10-00 



8-85 



4-65 



0-35 



Bottom. 



Mean temperature of the column of water, 105°-278. 



Thermometer No. 3, D 99-9 



Thermometer No. 3, B 113-7 



Thermometer No. 6, D 113-9 



From the water bubbling incessantly at the surface, we 



