“So far as observed, the temperature rose very nearly in proportion to the depth of the well, from about 188° at the top to about 260° at the bottom.”
The following are the temperature measurements at the Great Geyser, taken on August 6 and 7, 1874, and given on April 29, 1875, at the Royal Society of Edinburgh by Robert Walker, Esq., a Fellow of the Society:
| Depth in feet from surface. | Observed temperature (Fahr.). |
| 0 = | 187° |
| 10·5= | 190° |
| 18 = | 197° |
| 27 = | 211° |
| 36 = | 243° |
| 39 = | 247° |
| 45 = | 250°·5 |
| 49·5= | 254° |
| 54 = | 256°·5 |
| 58·5= | 254° (?) |
| 67·5= | 259°·5 |
| 77·5= | 257° |
“As an example of change in these springs: on the first visit, a pool was found near the Little Geyser, from which a stream ran eastwards, the temperature on the surface was 168°; adhering to the sides thick fleshy leaves of Algæ of a greenish-brown colour were floating. The spot was marked, and three years after, the Algæ were gone, all but a little on the sides, the temperature reduced to 139°, the water had sunk down, and the stream had ceased, leaving its former course quite discernible by the grass which covered it being of a lighter green tint than that on each side of its course. To the west, steam issued out of a minute hole: a stroke of the hammer disclosed a little pool in ebullition, but the temperature was only 184°. Is this little fellow destined at some future day to rival his companions?
“Between the Geyser and the beautiful caverns often described there is an ugly hole about 8 feet diameter, most dangerous, and horrible to look at; unlike all the rest, containing the purest water, it is filled to within 4 or 5 feet of its mouth with a silicious paste of a dark-brown colour, of the consistency of porridge, alternately popling and boiling furiously.
“Visiting Reykir in 1858, we were informed by the pastor that the period of its Geyser was just six hours, so we had but an hour to wait. True to time, the water gradually rose with a continuous flow, rising higher and higher during a space of twenty minutes, until it had reached a height of 38 feet. A little instrument, designed by the Astronomer Royal for Scotland, with the aid of a friend from Bo’ness, was sufficient to give this close approximation.
“The charm of the Geyser at Reykir could not be exceeded; the shafts, as they rose, curved outwards all round in perfect symmetry, a tree of live water, throwing off steam, but not sufficient to obscure its marvellous beauty, as the sun played and sparkled among its branches.
“It is difficult to account for these various phenomena.
“Place a glass tube half filled with water over a lamp or gas light. After the water is boiled, it will be ejected by successive spurts; and looking at the bottom of the tube, an air space will be seen, expanding as the water is ejected. This is the explosive material so often referred to, and it is upon this operation that the diminutive Geysers have been constructed to so far explain the action and time of these water volcanoes.