This second volume presents basic elements of physical oceanography in relation to the observations of the H.M.S. Challenger. Our approach is built around W.B. Carpenter’s idea, which advocated that the temperature distribution in the ocean was closely related to the world ocean circulation and that it might be possible to have a better understanding of the global currents from an accurate temperature measurement. After a history of underwater temperature measurement techniques, we introduced general concepts of geostrophic flow and developed a simplified model of the thermocline by introducing some original formulations. We concluded with more general notions concerning the wind effect, the water body transport, the coupling between the oceanic layers (OML, geostrophic and bottom boundary layers) and the thermohaline circulation.

We also noted the relevance of the Challenger’s physical observations and particularly the temperature measurements that are very consistent with the proposed models and with more recent oceanographic surveys.

Volume 2 only partially deals with the subject and does not in itself constitute a complete treatise on oceanography. However, its deliberately pedagogical approach to concepts and basic notions and, in addition, the comparison of modeling and experimental results (from Challenger data and the EPIC database) should help students in fluid mechanics and physical oceanography in their study of these disciplines.

General equations of motion	[3.20–3.24]
Equation of state	[3.25bis]
Characteristic scale of depth	[3.33]
Vertical velocity at the base	[3.35]
Temperature at the top	[4.37bis]
Density evolution equation	[4.39]
Temperature evolution equation	[4.40]

Wind stress	[4.27 sphere]
Vertical velocity at the base	[4.35]

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1. Foreword
2. Preface
3. Chapter 1. Background and Challenges of Submarine Exploration in the 19th Century
   1. 1.1. Submarine exploration
   2. 1.2. Means of communication in the 19th Century: birth of the telegraph
      1. 1.2.1. Aerial optical telegraph
      2. 1.2.2. Electric telegraph
   3. 1.3. Establishment of the first international telecommunications network
      1. 1.3.1. National links, overhead cables
      2. 1.3.2. International links and submarine cables
      3. 1.3.3. Expansion of the global telegraph network
   4. 1.4. Economic and political contexts of England in the 1870s
4. Chapter 2. Sailors and Scientists of the H.M.S. Challenger
   1. 2.1. Introduction
   2. 2.2. Biographies of the Royal Navy officers
      1. 2.2.1. George Henry Richards
      2. 2.2.2. George Strong Nares
      3. 2.2.3. Frank Tourle Thomson
      4. 2.2.4. John Fiot Lee Pearse Maclear
      5. 2.2.5. Thomas Henry Tizard
      6. 2.2.6. Pelham Aldrich
   3. 2.3. Biographies of the scientific team
      1. 2.3.1. William Benjamin Carpenter
      2. 2.3.2. Charles Wyville Thomson
      3. 2.3.3. John Murray
      4. 2.3.4. Henry Nottidge Moseley
      5. 2.3.5. Rudolf von Willemoës-Suhm
      6. 2.3.6. John Young Buchanan
      7. 2.3.7. John James Wild
   4. 2.4. List of officers, scientists and members of the technical, medical and administrative bodies of the Challenger expedition when departing from Portsmouth, on December 21, 1872
5. Chapter 3. Narrative Summary of the H.M.S. Challenger Cruise
   1. 3.1. Introduction
   2. 3.2. Explorations in 1873
      1. 3.2.1. North Atlantic Ocean
      2. 3.2.2. South Atlantic Ocean
      3. 3.2.3. Indian Ocean
   3. 3.3. Explorations in 1874
      1. 3.3.1. Indian Ocean
      2. 3.3.2. South Pacific Ocean – Tasman Sea
      3. 3.3.3. Central Pacific Ocean
      4. 3.3.4. North Pacific Ocean
   4. 3.4. Explorations in 1875
      1. 3.4.1. Central Pacific Ocean
      2. 3.4.2. North Pacific Ocean
      3. 3.4.3. Central Pacific Ocean (Tahiti)
      4. 3.4.4. South Pacific Ocean
   5. 3.5. Explorations in 1876
      1. 3.5.1. South Pacific Ocean
      2. 3.5.2. South Atlantic Ocean
      3. 3.5.3. North Atlantic Ocean
   6. 3.6. Epilogue of the cruise
6. Chapter 4. Scientific Equipment and Observations of the H.M.S. Challenger
   1. 4.1. Introduction
   2. 4.2. The H.M.S. Challenger and its scientific facilities
      1. 4.2.1. Refurbishment of the upper deck
      2. 4.2.2. Refurbishments of the main deck
      3. 4.2.3. Refurbishment of the lower deck and the hold
   3. 4.3. Dredging and sounding instruments
      1. 4.3.1. Dredges and trawls
      2. 4.3.2. Accumulators
      3. 4.3.3. Hydra Sounding Machine
   4. 4.4. Dredging, trawling and sounding methods
      1. 4.4.1. Dredging and trawling methods
      2. 4.4.2. Method of sounding
      3. 4.4.3. Precision and uncertainty in depth measurement
   5. 4.5. Immersion speed of a sounding apparatus
      1. 4.5.1. Free fall of the Hydra Sounding Machine
      2. 4.5.2. Fall of the Hydra Sounding Machine connected to the line, under constant external tensile strength
      3. 4.5.3. Observation of the entrance of the line in water
   6. 4.6. Contribution of the H.M.S. Challenger’s expedition to knowledge of seabed relief
      1. 4.6.1. Summary of current knowledge relating to the Earth and the geomorphology of the seabed
      2. 4.6.2. Examples of bathymetric surveys illustrating the different types of seabed relief
   7. 4.7. Observation of the ocean waters during the expedition of the H.M.S. Challenger
      1. 4.7.1. Methods and instruments of measurement
      2. 4.7.2. Examples of measurements
7. Conclusion