on the "principal Geijsirs of Iceland. 



399 



The mean temperature of the column of water was ob- 

 tained by multiplying half the sum of the indications of two 

 consecutive thermometers, by the interval which separates 

 them, and dividing the sum of all these products by the sum 

 of the intervals, or the length of the line. 



Twelve minutes after the fourth experiment, at 7^ 'tO'" in 

 the evening, the great eruption took place. 



The following are the results of the fifth experiment com- 

 menced the 7th July, at 9'' 45'" in the evening, two hours after 

 the great eruption ; basin half-filled : height of the liquid 

 column, 22"»-75; length of the line, 22^-50. Heights. 



„ m 



85-0 22-50 



. 103-0 13-50 



. 121-0 9-70 



. lost 4,-90 



. 122-5 0-30 



Bottom. 



Mean temperature of the column of water 108°-83. 

 The three preceding tables show, in an evident manner, 

 that the mean temperature of the column of water which fills 

 the central well of the Great Geysir, remaining in other re- 

 spects constant, the distribution of the temperature, in dif- 

 ferent points of that column, varies with the moment when 

 the observation was made. We see, on examining these 

 tables, that there is at the bottom of the well a maximum, im- 

 mediately before the eruptions, which may be estimated at 

 127°; and a minimum, immediately after, which may be esti- 

 mated at 123°. 



I'he results given in the two following tables, obtained at 

 different periods between two consecutive eruptions, show 

 that the phaenomenon always passes in the same manner, and 

 with tolerable regularity: — 



Thermometer No. 1, D 

 Thermometer No. 3, D 

 Thernionieter No. 5, D 

 Thermometer No. 6, D 



First Experiment. 

 The Cth July, at 0'> 30"" in the morn- 

 ing : three lioiirs after a great erup- 

 tion, and eleven hours before the 

 following eruption. JJasin half-full : 

 height of the liquid column, 22'"-75. 



Second Experiinent. 

 The 6th July, at 8* 20"' in the morn- 

 ing : nuie hours after a great erup- 

 tion, and twenty-three hours before 

 thefollowing eruption. Basin tilled: 

 height of the column, 23"'-50 ; 

 length of the line, 22'"-85. 



Heights, 



85-0 



Therm. No. 6, D 82-6 



Therm. No. 5, I) 85-8 



Therm. No. 2, iJ 113-0 



Therm. No. 3, D 122-7 



Therm. No. 1,13 123 6 



Heights, 

 m 



22-85 



19-20 



14-40 



9-60 



4-80 



0-30 



Bottom 



Mean temperature of the column of 

 water, 102<'-30. 



