58 FRIDTJOF NANSEN. M.-N. Kl. 
is probable that these features may be made out by studying critically 
the material at hand. 
The following expeditions have made observations which may be 
valuable from this point of view. 
The Norwegian North Atlantic Expedition, on board the Vöringen 
took a great many Stations in the region east and northeast of Amund- 
sen's Stations, in July and August, 1878. The temperatures, given by 
Prof. Mohn! seem to be fairly trustworthy wherever they have been 
gradually decreasing from the surface downwards, but where, in the 
upper water-strata, a warmer layer has been placed under a colder one, 
a feature very characteristic for Artic waters, the instruments used have 
not given trustworthy results, and frequently have even failed to indi- 
cate the excistence of such warm layers, which are now known to exist. 
The reversing apparatus used, a wooden case, did not give the Negretti 
and Zambra thermometers a sufficient time for assuming the correct 
temperature, since the instruments were frequently reversed as soon as 
they reached their proper depth, and the readings obtained were therefore 
more or less due to the temperature of water-strata through which the 
thermometers had passed on their way down, and not so much the 
actual temperature at the depth recorded. The other thermometers used 
during the expedition have evidently not been suitable for measuring 
accurately the temperatures of such intermediate warm water-strata. 
Mohn’s curves, representing the vertical distribution of temperature, 
have, at many Arctic Stations (e. g. Stations 226, 297, 298, 300, 304, 
350, 351, 352), indications of the typical warmer water-stratum under- 
lying the cold Polar layer near the surface, but it must be assumed that 
the temperatures of this particular warm stratum are in most cases too 
low. It is therefore often somewhat difficult to use the temperatures for 
comparasion with more accurate observations. The salinities or specific 
gravilies obtained for deeper water-strata during this expedition, are not 
sufficiently trustworthy for the present purpose. 
Captain C. Ryder?, on board the Hekla, took in July 1891, a 
series of very important Stations (R VIII—R XII, Pl. V) across the 
East Greenland Polar Current, north of Amundsen’s Stations. Ryder’s 
temperatures were taken with Negretti and Zambra Reversing Thermo- 
meters, and are evidently fairly good. But the values af salinity are not 
' H. Mohn, The North Ocean. its Depths, Temperature and Circulation, The Norwegian 
North- Atlantic Expedition, 1876—1878, Christiania, 1887. 
? C. Ryder, Den Østgrønlandske Expedition, 1891—92, Meddelelser om Grønland, vol. 
XVII, Copenhagen, 1895, pp. 189 et seq. 
