396 M. Descloizeaux's Physical and Geological Observations 



The two jetting springs, the temperatures of which I have 

 principally sought to determine during my stay in that locality 

 with M. Bunsen of Marburg, are the Great Geysir and the 

 Strokkur. I shall first direct my remarks to the Great Geysir. 



The only observations of any accuracy which we hitherto 

 possessed on the temperature of this spring are those of 

 M. Lottin, a member of the Northern Scientific Commis- 

 sion, who visited Iceland in 1 836 ; but these observations left 

 much still to be desired, both from the method itself which 

 M. Lottin followed, and from the experiments not having 

 been sufficiently repeated to embrace the various phases of 

 the moments of calm and of eruptions of the geysir. The 

 determinations which M. Bunsen and I have made were taken 

 immediately before a great eruption, immediately after that 

 eruption, and in the interval of two great consecutive erup- 

 tions. The thermometers which I employed were double- 

 bulbed, and constructed by Bunten after the directions of M. 

 Kegnault*: they were composed of a small cylindrical reser- 

 voir, surmounted by a stem of accurate calibre, and divided 

 into parts of equal capacity ; this stem ended in a finely drawn- 

 out point terminating almost at the summit of a small cap of 

 thin glass, soldered to the top of the stem, at the part where 

 its diameter began to diminish, and containing a small excess 

 of mercury. 



In taking observations with these thermometers, the stem 

 was entirely filled with mercury, at the ambient temperature ; 

 it was then immersed, by the side of a good standard, in a 

 bath, the temperature of which was nearly constant, and lovier 

 than that which was to be observed : a portion of the mercury 

 of the stem was raised into the small upper bulb. When the 

 mercury was stationary and occupied exactly the extremity of 

 the small drawn-out point, the temperature of the standard 



formed in a given time, to establish at tlie Geysir itself a fixed mark capable 

 of resisting the ignorant curiosity of certain visitors, I endeavoured to con- 

 struct one easy to be recognised only by the forewarned and attentive eye. 

 For this purpose, I chose two contiguous latigs, situated at nearly an equal 

 distance from the Strokkur and the Geysir, proceeding towards theLaugaf- 

 jall : the most northern laiig, without apparent overflow, is contained in a 

 nearly elliptical basin, the major axis of which is seven metres, the minor 

 one 3'"-40, and the depth S^-SS ; the temperature at the surface was 

 found to be 98^-5. The second laiig, separated only from the first by a 

 small natural wall, has a more irregular basin, of a depth of 9™-30,and the 

 water of which, indicating a temperature of 96''-5, flows off incessantly by 

 a small rivulet which passes near the Strokkur, depositing on its way abun- 

 dant incrustations. In the narrowest part of the wall which separates these 

 two laugs I made an aperture, the successive obliteration of which it will 

 always be easy to ascertain. The following were the dimensions of this 

 aperture on July 12th, 1846: — Depth 0"'-OG5 j length, from east to west, 

 0'"-2G0; breadth, from north to south, 0"i-110. 

 * See Scientific Memoirs, Part XVI. p. 588- 



