294 KEPOET OF COMMISSIONER OF FISH AND FISHERIES. 



anchored ship it is comparatively easy to determine the surface-current, 

 but not when the vessel is in motion, especially as regards the determi- 

 nation of the under current. On a firm position or from an anchored 

 ship, the Commission made use of a simple apparatus consisting of two 

 metallic plates combined crosswise and fastened by a fine wire. The 

 current pressing against the plates shifts them from a horizontal i)osition, 

 and thus the strength of the current is approximately determined by 

 angle of deviation. This instrument, however, is not sufficiently sensi- 

 tive for a weak current, and does not admit of an exact determination 

 of the velocity. Floating bodies combined with the plates also worked 

 unsatisfactorily for the under currents, the upper currents interfering 

 with the indication of the instrument 5 it was found to be perfectly useless 

 when the ship was in motion or when drifting with the current. As the 

 determinations of velocity and direction of these currents are of great 

 importance, the invention of a good current-meter is very desirable. 



Deep-sea investigations proper have been made by the Commission only 

 in a hmited sense ; the greatest depths investigated were in the Baltic 

 amounting to less than 200, and in the German Ocean to less than 400 

 fathoms. In such depths it is not difficult to manipulate the instruments. 

 The determination of depth can be made by simple means ; the bringing 

 up of bottom may be done by dredging. Should the Commission have oc- 

 casion to make more extended investigations of the German Ocean cur- 

 rents, or the ^avy enter upon such scientific labors, it would be desirable 

 to introduce improvements in the measurement of depths, the apparatus 

 thus far employed not being sufficiently accurate. For trustworthy de- 

 terminations an apparatus operated by the pressure of the water is 

 required. Some instruments have been constructed upon the principle 

 of Mariotte's law of compressed air, but they are not sufficiently sensi- 

 tive. It would probably be best to make use of spring-manometers 

 constructed for high pressures of the ocean depths. The knowledge of 

 temperatures and percentage of salt will be highly valuable only in con- 

 nection with exact measurement of depth. 



The Commission hopes that the government will continue the means 

 for carrying on the investigation in question. When the expeditions 

 become more frequent and numerous, and the Navy and commercial ships 

 participate, science cannot fail to be considerably enriched by important 

 results. There will then be occasion to solve many more interesting 

 problems not thus far studied, for instance the changes in the mean level 

 of the ocean, or the secular changes in the level of the coast, the question 

 of the intensity of light in various depths of the water, etc., etc. 



