436 Proceedings of the Royal Society 
north to south and breadth from east to west were found to be 
equal, and 8| miles respectively, while the total area, with less 
than 100 fathoms of water on it, was 50 square miles. A 
boat was anchored in the noon position of the 21st October — 
namely, lat. 31° 9' 30" 1ST., long. 13° 34' 30" — in 58 fathoms of 
water. This is near the centre of the bank, and a little to the south- 
ward of the shoalest sounding, 49 fathoms ; swabs had been attached 
to the mooring rope of the buoy ; they had also been attached to 
the moorings of a couple of balloon buoys in rather shallower water, 
but during the two days that they were down the ropes got so 
chafed that they broke when being recovered. Swabs had been 
attached to the boat’s cable, and they were recovered, but, as they 
had been only a very short time on the bottom, little was expected 
and little was found on them. A few broken and decayed shells 
made up the harvest. 
Advantage was taken of the buoy being anchored in mid-ocean to 
make some current observations. It is an almost universal ex- 
perience of ships making a passage from the north to the Canary 
Islands to be set very considerably to the eastward of their course, 
and many disastrous shipwrecks have been the consequence. It 
appears from recently-collected observations that the general set of 
the current is about E.S.E., and its velocity averages 16 miles 
per day. Only a few weeks previously a buoy belonging to the 
United States Lighthouse Department had been washed ashore on 
the north coast of Teneriffe. Knowing how the tidal wave is trans- 
formed into a current on approaching the coast, it seemed not 
unlikely that the occurrence of so extensive a shoal as the “ Dacia 
bank,” as it has been called according to recognised precedent, 
might produce the same effect. Accordingly, before the buoy was 
brought on board again, I spent some hours in a boat riding to it, 
and determined the direction and rate of the surface current at fre- 
quent intervals, while the ship went on with the sounding at a 
distance. The result of these observations was, shortly, to show 
that the south-easterly current in this part of the ocean is affected 
and at times reversed by a tidal current. Down to a depth of 
70 fathoms the current was found to be setting in nearly the same 
direction as at the surface, but with somewhat greater strength. 
The “ current drag ” used on this occasion was a “ tow-net ” made of 
