12 THYSICAL GEOGRArnY OF THE SEA, AND ITS METEOROLOGY. 



year come round, and the surplus temperature, thus withdrawn 

 and stored away at the time it might have proved superfluous 

 or inconvenient, is rendered back so soon as it is required ; 

 thus the cold of night and the rigour of winter are modified by 

 the heat given out at the point of condensation by dew, rain, 

 hail, and snow. 



35. Effects upon the earth. — " The earth is a bad conductor of 

 heat ; the rays of the sun, which enter its surface and raise the 

 temperature to 100° or 150°, scarcely penetrate a foot into the 

 ground ; a few feet down, the warmth of the ground is nearly 

 the same night and day. The moisture which is there preserved 

 free from the influence of currents of air is never raised into 

 vapour;' so soon as the upper stratum of earth becomes tho- 

 roughly dried, capillary action, hj means of which all excess of 

 water was withdrawn, ceases ; so that, even under the heats of 

 the tropics, the soil two feet down will be found, on ihe approach 

 of the rains, sufficiently moist for the nourishment of plants. 

 The splendid flowers and vigoro^^s foliage which burst forth in 

 May, when the parched soil would lead us to look for nothing 

 but sterility, need in no way surprise us ; fountains of water, 

 boundless in extent and limited in depth only by the thickness 

 of the soil which contains them, have been set aside and sealed 

 up for their use, beyond the reach of those thirsty winds or burn- 

 ing THjs which are suffered to carry off only the water which is 

 superfluous, and would be pernicious. They remove it to other 

 lands, where its agency is required, or treasure it up, as the ma- 

 terial of clouds and dew, in the crj^stal vault of the firmament, 

 the source, when the fitting season comes round again, of those 

 deluges of rain which provide for the wants of the year. Such 

 are some of the examples which may be supplied of general laws 

 operating over nearly the whole surface of the terraqueous globe. 

 Among the local provisions ancillary to these are the monsoons 

 of India, and the land and sea breezes prevalent throughout the 

 tropical coasts. 



3G. The tides. — " We have not noticed the tides, which, obe- 

 dient to the sun and moon, daily convey two vast masses of 

 water round the globe, and which twice a month, rising to an 

 unusual height, visit elevations which otherwise are dry. During 

 one half of the year the highest tides visit us by day, the other 

 half b}^ night ; and at Bombay, at spring tide, the depths of the 

 two difi'er by two or three feet from each other. The tides 



