GULF STREAM, CLIMATES, AND COMMERCE. 53 



jectile that distance through either air or water. The power 

 that conveys the waters of the Gulf Stream across the ocean is 

 acting upon them (§ 95) every moment, like gi-avity upon the 

 current of the Mississippi river ; with this difference, however, 

 the Mississippi runs down hill, the Gulf Stream on the dead 

 level of the sea. But if we appeal (§ 80) to salt and vapour, to 

 heat and cold, and to the secreting powers of the insects of the 

 sea, we shall find just such sources of everlasting changes and 

 just such constantly acting forces as are required (§ 108) to keep 

 up and sustain, not only the Gulf Stream, but the endless round 

 of currents in the sea, which run from the equator to the poles, 

 and from the poles back to the equator ; and these forces are 

 derived from difference in specific gravity between the flowing 

 and reflowing water. 



147. Tlie true cause of the Gulf Stream. — The waters of the Gulf 

 as they go from their fountain have their specific gravity in a 

 state of perpetual alteration in consequence of the change of salt- 

 ness, and in consequence also of the change of temperature. In 

 these changes, and not in the trade-winds, resides the power 

 which makes the great currents of the sea. 



CHAPTER III. 



§ 150-191. — INFLUENCE OF THE GULF STREAM UPOX CLIMATF^ AND 



C0M]\rERCE. 



150. JSoiu the Washington Observatory is warmed. — Modern inge- 

 nuity has suggested a beautiful mode of warming houses iu 

 winter. It is done by means of hot water. The furnace and 

 the caldron are sometimes placed at a distance from the apart- 

 ments to be warmed. It is so at the Washington Observatory. 

 In this case, pipes are used to conduct the heated water from 

 the caldron under the superintendent's dwelling over into one o1 

 the basement rooms of the Observatory, a distance of one 

 hundred feet. These pipes are then flared out so as to present 

 a large cooling surface ; after which they are united into one 

 again, through which the water, being now cooled, returns 

 of its own accord to the caldron. Thus cool water is returning 

 all the time and flowing in at the bottom of the caldron, while 

 hot water is continually flowing out at the top. The ventilation 



