HYDROGR. SECTION — APPENDIX D ( 50 ) 
The methods of hydrographic investigation in use on board the steamers 
and in the laboratories, as well as the collection and utilisation of all other hy- 
drographical material are now so developed and systematized that we may rest 
assured that future hydrographic investigations will proceed on coordinated lines. 
This is further indicated by the circumstance that the hydrographical methods in 
use in the International cooperation have been, for the most part, adopted by 
recent scientific expeditions. 
On the methods, and especially on the results obtained, a considerable litte- 
rature is already available. 
Results of the Investigations 
A. Hydrographic Researches 
I. The Baltic: 
With regard to the Baltic proper, together ich the Gulf of Bothnia and the 
Gulf of Finland, the following results may regarded as definitely established: 
The water is subject to a great movement of circulation, which goes on 
in the following way. Along the surface, sea-water of low salinity flows towards 
the outlets of the Baltic, especially along the Swedish coasts; while on the”other 
hand water of relatively high salinity flows in along the bottom. In the south- 
western part of the Baltic, as a general rule, this bottom-current proceeds irregu- 
larly and at intervals, while north of the Gotland Deep it is more steady and 
takes place chiefly along the southern and eastern parts of the basin. We are 
now in a position to give numerical data regarding these matters. 
A distinctly marked yearly periodicity is found to exist in the hydrographic 
conditions, (temperatures, salinities, and partly also gaseous contents), such that the 
differences between the upper water-layers and the bottom-layers increase from 
south to north during the summer, while during the winter an en may 
be noticed. 
In the deep portions of the middle part of the Baltic the salt water of the 
bottom-layer, which has been brought in by under-currents retains a comparati- 
vely high temperature during the winter months, when the funeste of the 
surface-layer is much diminished. | 
Besides this, the first step to obtain an exact knowledge of the surface 
currents, of great importance for navigation, especially in the areas under the 
investigation of Finland have now been made. 
II. Western part of the Baltic, the Belts, and the Cattegat: 
In these areas the water masses, which leave the Baltic with a relatively 
low salinity, and those which are flowing from the Skager Rak to the Baltic with 
