CONTENTS. xi 



SECTION IV. 



PAGE 



1. An Accoont of the Scattered Rocks, Shoals, and Vigias, in the 



North Atlantic Ocean. 



General Remarks 593 



Shoals, &c., to the Northward of Latitude 40° N 597 



Shoals, &c., between the Equator and Latitude 40° N 603 



Tables of Doubtful Rocks in the North Atlantic Ocean G08 



Table A, Rocks whose Existence is Very Doubtful, 608 ; 

 Table B, Rocks, &c., Reported, but do Not Exist, 609—611. 



2. Volcanic Regions 611 



3. Discoloured Water 615 



4. Palls op Dust in the North Atlantic Ockan 621 



5. Depth, Temperature, &c., of the North Atlantic Ocean 626 



Deep-Sea Sounding, 626 ; Deep-Sea Exploring Expeditions, 627 — 631 ; 

 Apparatus, 631 — 633 ; Depth, 633 ; Deep-Sea Deposits, 634. 



Temperature, 635 ; Thermometers, 635 — 639 ; The Temperature of the 

 Surface Water, 640—641 ; Of the Deep Sea, 641—642. 



Salinity and Specific Gravity of the Ocean, 642 — 646 ; Circulation of Ocean 

 Water, 646—648 ; Animal Life, &c., 648—652 ; Waves, 652—653. 



On the Use op Oil for Calming Rough Seas 658 



6. Classipication of the Clouds 658 



7. On Magnetism AND the Compass 663 



History and Principles, 663 ; Terrestrial Magnetism, 664 ; Variation, 

 666 ; Dip and Intensity, 667 ; Local Deviation, 668 ; Dr. Scoresby 

 on the Changes which take place in the Magnetism of Iron Ships, 

 669 — 671 ; Extracts from the Reports of Captain P. J. Evans on the 

 Compass, 671 — 675 ; On the Nature of the Magnetism in Iron Ships, 

 671 ; On the Best Direction for Building an Iron Ship, 672 ; On the 

 Position and Arrangement of the Compass, 672 ; On Various Sources of 

 Error, 673 ; ESect of Direction while Building, 675 ; The Heeling Error, 

 675 ; Sub-Permanent and Permanent Magnetism, 676; Local Derangements 

 of the Compass, 676 ; The Standard Compass, 676. 



8. Remarks on the Barometer, by Admiral FitzRoy and others 677 



Alphabetical Index 683 



