884 
THE VOYAGE OF H.M.S. CHALLENGER. 
statement which only rests on assertion without corroborative observation. No alteration 
could be detected by the eye in the heights of these numerous pinnacles, which appeared 
to be in exactly the same state as when this group was surveyed by Captains Fitz Roy 
and Sulivan in 1834-39. 
The assertion that no alteration could be detected by the eye was of course of no 
more value than that of the residents, who said that an alteration had taken place ; 
fortunately, however, Sir James Clark Ross, during his stay at the group in 1842 to refit 
the “Erebus” and “Terror” for another cruise to the southward, had taken tidal 
observations and left permanent marks on the rocks immediately adjacent to his 
observation spot. These marks, two in number, were made, one by levelling the 
top of a rock and the other by cutting a ledge in the face of a cliff, both 5 feet 8 inches 
above the mean level of the sea as deduced from five months observations. They are 
situated on the coast immediately to the westward of the small stream west of the 
entrance to the careenage basin of Port Louis, Berkeley Sound, so that a comparison could 
be made, with some degree of accuracy, of the state of the sea level now with that as 
determined by Sir James Ross thirty -four years previously. 
It was of course known that to make a really accurate comparison of the tidal wave 
and mean level of the sea now with the result deduced from the observations of Sir 
James Ross, a considerable time would be required ; for the whole question is so complex 
that observations extending over only a few tides are but of little value, and had it 
been requisite to investigate the point scientifically, arrangements should have been 
made for an accurate tidal and barometric register for a period which should embrace 
the months devoted by Sir James Ross to these observations at Port Louis. But when it 
is only necessary to ascertain within a few inches whether any alteration has taken place, 
the mean sea-level deduced from two or three successive tides, when the barometer is near 
its normal condition, is all that is requisite, and was all that was found necessary, for 
the mean result of two high and two low waters at Port Louis, during which time the 
barometer was steady at an average of OT of an inch above its mean height for the year, 
gave the mean level of the sea within an inch of Sir James Ross’s result, and just an inch 
less than his, corresponding precisely with the amount which should be allowed for the 
extra pressure of OT of an inch of the mercurial column. 
It may therefore be safely asserted that the inhabitants of Stanley were in error in 
supposing that they had detected an alteration in the level of the sea, for if any 
alteration had taken place it must have been far too slight to be noticed by casual 
observers. The fact is, that the observations of Sir James Ross at Port Louis, as well as 
those of the Challenger at Port Stanley, show certain irregularities of the tide which 
may easily be mistaken for alterations of sea level. Firstly, the diurnal inequality 
is considerable; on one occasion it amounted to feet at Port Stanley, that is, a 
difference of 3 feet in the range of the two tides, and the inequality disappears at neaps, 
