Physical Geography as a Popular Study. 63 



vernal equinox (or have been situated in long. 0°), and in long. 

 90° about A.D. 1250. In A.D. 11700, lie adds that "the ex- 

 treme summer and winter of the southern hemisphere will be 

 trausferred to the northern." Such changes must have taken 

 place thousands of times in geological eras, and may have 

 partially accounted for those changes of climate which geology 

 and palasontology show to have occurred. 



Terrestrial climate is still more strongly affected by the 

 disposition of masses of land and water, the height and direction 

 of mountain-chains, the character of the soil, its being covered 

 with trees or left bare, etc. Of the whole surface of the 

 earth ' ' only a fourth part, or about fifty- two millions of square 

 miles, rises above the uniform level of the water and form land," 

 and it is remarkable that a great part of this land " is grouped 

 round one hemisphere, so that not more than one twenty- 

 seventh part has land opposed to it on the opposite hemisphere. 

 Thus, if a person stationed vertically over Falmouth in England 

 could see half the globe, he would see more than forty-nine 

 out of the fifty-one millions of square miles of land, or about 

 an equal surface of land and water. If, however, he were 

 perched equally high above New Zealand, he would see ninety- 

 six and a half millions of square miles of water, and less than 

 two millions of square miles of land." 



Any important change in the relative proportions and dis- 

 positions of land and water would materially modify the earth* s 

 climate. Supposing the quantity of each within a moderate 

 number of miles from the surface to remain the same, but the 

 shallow seas to be considerably deepened and at the same time 

 narrowed, and the bulk of continuous continents very much 

 augmented, there would be a diminution of evaporation, and 

 an addition to excessive or continental climate. On the other 

 hand, rendering deep seas shallower, and diminishing the area 

 of land by a corresponding change in its level would produce 

 opposite effects, and the violence of the alteration would 

 depend partly on the average extent to which levels were 

 modified, still more on the position of the high lands. 



The laws which determine the relative disposition of land and 

 water are very little known ; and hence there is room for two 

 opposite suppositions, according to one of which the present 

 arrangement depends on permanent causes of very ancient 

 date ; and, according to the other, great changes may have 

 taken place within comparatively moderate periods, and equally 

 important alterations may still be going on, though their rate 

 may be very slow. Professor Ansted refers to a speculation of 

 Mr. James Yates, that the centre of gravity of the earth would 

 not be coincident with the centre of magnitude without the pro- 

 tuberance of water on one side, and that the inequality of land 



