TRANSACTIONS OF THE SECTIONS. 191 



Another point is the practicability of the Niger for navigation. It is now navi- 

 gable by steaniera for 500 miles, thence to Timbuctoo 1000, and above that may be 

 navigable for 500 more. 



A complete line of navigation from the Atlantic by the inland sea, a canal to 

 the Niger, and down the Niger, in all 2300 miles, woidd open the whole region. 



Mr. M'Kenzie proposes to go first to the coast and ascertain what he can 

 without penetrating far, then to return and report to the public, and propose 

 for a thorough exploration of the whole line from the Atlantic to Timbuctoo and 

 round to the Bight of Benin. 



There are probably twenty millions of people in North-western Africa, many of 

 whom would be affected by this enterprise. 



The probable ultimate effects of an inland sea on the surrounding country and 

 on South Europe is not the question at present; but we need information to jus- 

 tify us in further investigation. If the area is as great as represented, an immense 

 body of water would be required ; but while it was filling it would be available 

 so far as the water extended. 



The south side of this depression is a fertile and populous country with two large 

 towns, dividing the district into three portions of about 300 miles each ; so that 

 there does not appear any great obstacle to the land carriage. 



The point proposed to be occupied on the coast is at present without any 

 inhabitants, being south of the kingdom of Morocco, and there appears nothing in 

 the way of our establishing a depot there. 



The establishment of English missions and commercial depots on this line would 

 greatly support our operations on the Gold Coast. Both the colonial and foreign 

 offices have expressed an interest in the undertaking. 



On the ' Challenger's ' Crucial Test of the Wind and Gravitation Theories 

 of Oceanic Circulation*. By Jajtes Croll, of H.M. Geol. Survey. 



North Atlantic. — The researches of the ' Challenger ' expedition bring to light 

 the striking and important fiict that the general surface of the North Atlantic, to 

 be in equilibrium, must stand at a higher level than that of the ocean at the 

 equator. In other words, the surface of the Atlantic is lowest at the eqtiatoi-, and 

 rises with a gentle slope to well nigh the latitude of England — a residt which proves 

 the physical impossibility, in so fai- as the North Atlantic is concerned, of any 

 general interchange of equatorial and polar water due to gravitation. 



In order to establish this point a section was taken of the INlid-Atlantic, north 

 and south, across the equator, viz. that section adopted by Dr. Carpenter as the 

 one of all others most favom'able to the gi-avitation theory t- 



On looking at this section the author was forcibly struck that, if it was accu- 

 rately di-awn, the ocean, to be in eqmlibrium, would require to stand at a higher 

 level in the North Atlantic than at the equator. To determine whether such was 

 the case or not the temperatm-e-soundings indicated in the section were obtained 

 from the Hydi-ographer of the Admiralty. The following Table (p. 192) gives the 

 soundings in question at three stations — the first (A) at latitude 38° N., the second 

 (B) at latitude 23° N., and the third (C) at the equator. 



On computing the extent to which the three columns A, B, and C are each 

 expanded by heat, accordipg to Mimcke's Table of the expansion of sea-water for 

 every degree Fahrenheit, lit was found that column B, to be in equilibrium with 

 column C (the equatoriaJ»WJiumu), would require to have its siu-face standing 

 2 feet 6 inches above the level of column C, and column A fully 3 feet 6 inches 

 above that column. In short, there must be a gradual rise from the equator to 

 latitude 38° N. of 3^ feet. Professor Hubbard's Table of expansion gives almost 

 the same result. Difference in salinity of the columns produces scarcely any 

 sensible effect. 



* Published in extenso in the ' Philosopliical Magazine ' for September 1875. 

 t Proc. Roy. Geog. Soc. vol. xviii. p. 362. 



