EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC CIRCULATION.—DR. CARPENTER’S THEORY. Gulf-stream according to Dr. Carpenter not due to Difference of Specific Gravity.—Facts to be Explained.—The Explanation of the Facts.—The Explanation hypothetical.—The Cause assigned for the hypothetical Mode of Circulation.—Under Currents account for all the Facts better than the Gravitation Hypothesis.—Known Condition of the Ocean inconsistent with that Hypothesis 122 CHAPTER IX. EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC CIRCULATION.—THE MECHANICS OF DR. CARPENTER’S THEORY. Experimental Illustration of the Theory.—The Force exerted by Gravity.—Work performed by Gravity.—Circulation not by Convection.—Circulation depends on Difference in Density of the Equatorial and Polar Columns.—Absolute Amount of Work which can be performed by Gravity.—How Underflow is produced.—How Vertical Descent at the Poles and Ascent at the Equator is produced.—The Gibraltar Current.—Mistake in Mechanics concerning it.—The Baltic Current 145 CHAPTER X. EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC CIRCULATION.—DR. CARPENTER’S THEORY.—OBJECTIONS CONSIDERED. _Modus Operandi_ of the Matter.—Polar Cold considered by Dr. Carpenter the _Primum Mobile_.—Supposed Influence of Heat derived from the Earth’s Crust.—Circulation without Difference of Level.—A Confusion of Ideas in Reference to the supposed Agency of Polar Cold.—M. Dubuat’s Experiments.—A Begging of the Question at Issue.—Pressure as a Cause of Circulation 172 CHAPTER XI. THE INADEQUACY OF THE GRAVITATION THEORY PROVED BY ANOTHER METHOD. Quantity of Heat which can be conveyed by the General Oceanic Circulation trifling.—Tendency in the Advocates of the Gravitation Theory to under-estimate the Volume of the Gulf-stream.—Volume of the Stream as determined by the _Challenger_.—Immense Volume of Warm Water discovered by Captain Nares.—Condition of North Atlantic inconsistent with the Gravitation Theory.—Dr. Carpenter’s Estimate of the Thermal Work of the Gulf-stream 191 CHAPTER XII. MR. A. G. FINDLAY’S OBJECTIONS CONSIDERED. Mr. Findlay’s Estimate of the Volume of the Gulf-stream.—Mean Temperature of a Cross Section less than Mean Temperature of Stream.—Reason of such Diversity of Opinion regarding Ocean-currents.—More rigid Method of Investigation necessary 203 CHAPTER XIII.