on the principal Geysirs of Iceland. 

 Table (continued). 



403 



The heights of the two most remarkable eruptions during 

 our visit to the Geysir, measured by M. Sartorius von Wal- 

 tershausen with a theodolite, gave — 



The 6th of July, at 11^ OO'" a.m., 145 French ft. = 47'^"101. 

 The 14th of July, at 'S^ IS"* a.m., 152 French ft. = 49'^-375. 



I have said, at the commencement of this memoir, that the 

 water, when it had completely left the basin, after the great 

 eruptions, descended into the central well, at about 2^-50 be- 

 low its orifice. The following are two numbers I observed: — 



The 11 ih of July, at 6 o'clock in the evening, a depth 



of water below the orifice of the well 2'"'00 



The 14th of July, at 3'' 15'" in the morning f • • 2^60 



• The great eruptions are denoted by an •• 



t If we calculate the quantity of water which, to produce this lowering, 

 escaped from the basin, during and after the eruption, to flow almost 

 wholly into the Beina, we find that this quantity was, in the first case, 

 157""^^ 58.^, and, in the second case, l(Jl""-825: now, admitting that at 

 l.'J.j -8 and under the pressure of three atmospheres, the steam has n 

 volume equal to 600 times that of the water which produced it, and a 

 density of 00()1(!145, a quantity of vapour represented by !)4,.5.'jl cubic 

 metres = 162,Go2 kilograinincs in the first case, and by 97|095 cubic 

 2 E2 



