INTRODUCTORY ESSAY. 77 



The whole of Continental India lies north of the equator, 

 and considerably more than half of its area north of the 

 Tropic of Cancer, whose position very nearly corresponds 

 with the base of the peninsula of Hindostan. Proceeding 

 northwards from the tropic, there is no sea nearer than the 

 Arctic Ocean; but as we advance towards the equator the 

 width of the land gradually diminishes both in the Madras 

 and Malayan peninsulas. It may be observed also, that due 

 south of India, the ocean extends without interruption be- 

 yond the Antarctic Circle, while to the eastward, not only 

 on the equator but in the southern hemisphere, there is 

 much land. The Eastern Archipelago, from consisting of 

 large islands, separated by belts of sea, possesses a humid and 

 equable climate ; but the great continent of Australia, being a 

 vast expanse of low land, becomes enormously heated when 

 the sun is in the southern hemisphere, and presents extremes 

 of climate. To the westward the coast-line of Beluchistan 

 continues somewhat north of the tropic till it enters the Per- 

 sian Gulf; but the great continent of Arabia advances far 

 within the tropic ; while, a little further west, Africa extends, 

 uninterrupted by sea, far into the south temperate zone. From 

 this relative position of land and sea, it is evident that the 

 whole of the rain which falls in India must be derived from 

 the southward or eastward, and that those parts only can be 

 subject to heavy rains, towards which the sea- wind blows. 



The maps of the montlily isothermals*, recently published 

 by Dove, enable us to trace with considerable accuracy the 

 periodical changes of temperature throughout India and the 

 neighbouring countries. An inspection of these maps shows 

 us that in January the isothermal lines in the northern he- 

 misphere are nearly parallel to the equator, but that, m the 

 southern, Africa and Australia are preternaturally hot. Till 

 the vernal equinox, the equator of heat (or that line from 

 which the temperature diminishes both towards the north and 

 towards the south) lies south of the terrestrial equate! but 



* See Mods of Isothermal* appended to this Essay. 



