520 Proceedings of the Royal Society 
between 28 feet and 27 feet, 14° F., the rise between 27 feet and 
36 feet is as much as 32°. I regret that I did not observe this 
so as to interpolate one or two additional observations between 
these. But Bunsen’s results (vide 3d col.) give one intermediate 
measurement, his others being in remarkable accordance with 
mine. 
We had several displays of the power of Strokkur, a smaller 
G-eysir about a 100 yards from the Great G-eysir. Unlike the latter, 
it can be made to erupt by throwing in turf, stones, or earth, which 
stop up the funnel at a point about 27 feet down, where it narrows 
from a width at the mouth of about 8 feet to about 8 inches. The 
people living at the farm-house asserted that the long interval of 
inaction of the Great Geysir was owing to the very frequent erup- 
tions of Stokkur, which had been provoked by way of display during 
the king’s visit. 
Professor Tait has suggested the use of a thermo-electric 
junction, after Becquerel’s method, to determine with perfect 
accuracy the temperature at any point of the column. I believe, 
however, that no care in packing would make it possible to trans- 
port safely a galvanometer and a thermo-electric arrangement over 
80 miles of such country as one has to travel to the Great Geysir. 
I had the misery of seeing the package containing my thermometer 
repeatedly tossed from the pack-saddle, without any injury to the 
instrument, however, as I found by comparing it carefully on my 
return with one tested at Kew. The packages are fastened usually 
with hair ropes, and not only are these constantly getting loose, 
but, when a marrow part of the way is reached, the ponies, urged on 
behind by their drivers, charge against each other, and often leave 
their loads behind ere they get through. 
Setting out from the Geysir at 1 p.m. on Friday (7th August), I 
reached Reykjavik at 6 the following evening, and, I confess, was 
grievously disappointed to find that our steamer was not to sail for 
other 48 hours, an interval which would have sufficed to complete 
my observations, and would, most probably, have given me an 
opportunity of witnessing an eruption of this world-renowed spring. 
2. On the Capillary Surface of Revolution. By 
Sir William Thomson and Mr John Perry. 
