32 Original Articles. [Jan., 



in fact, to produce an extreme rather than an equable climate, a thermal 

 condition more trying to the health than perhaps any other. 



Nor should it be forgotten that, on account of the elliptical form 

 of the earth's orbit, the proximity of the perihelion to the winter 

 solstice, the greater amount of land on the Northern than on the 

 Southern side of the equator, and sundry other circumstances into 

 which it is unnecessary to enter here, the temperature of the Northern 

 hemisphere is less extreme in its fluctuations, and on the average is 

 higher than that of the Southern. 



There is an advantage, too, in our being on the eastern side of the 

 Atlantic. A line drawn round the earth, through all places having 

 the same mean annual temperature, is termed an isotherm. Now, 

 lines of this character, instead of coinciding with parallels of lati- 

 tude, undergo remarkable deflections ; for example, the isotherm of 

 50° Fahr. passes from the Pacific to the continent of Asia in about 

 latitude 42^ N. ; it gradually creeps up to 47£ N. between the Aral 

 and Caspian Seas, whence it ascends more rapidly, and enters the 

 German Ocean in about 53° N. ; it reaches its highest point in the 

 British Isles, where it touches the parallel of 54° N. ; after this it 

 bends southward, until, on entering the American continent, it almost 

 reaches the low latitude of 4.0° N. In its course across America, its 

 deflection, on the whole, is northerly ; and on the eastern side of the 

 Pacific it culminates a second time in 54° N. ; after which it bends 

 southwards, and reaches 4l£° N., in the Japan Archipelago. In 

 general terms, then, the greatest northern deflections occur on the 

 eastern, and the greatest southern deflections on the western, sides of 

 the two oceans, and this is true of all the isothermal lines north of 

 the tropic of Cancer ; so that the eastern sides of the Atlantic and 

 Pacific Oceans are warmer, and the western colder, than is due to 

 latitude merely. In the example traced above, the mean annual tem- 

 perature of Britain is the same as that of a place fourteen degrees 

 farther south on the opposite side of the Atlantic. 



But whence this difference ? 



Enormous bodies of water move through the ocean in constant 

 and definite directions ; some of them from tropical regions towards 

 the poles, others from cold latitudes towards the equator. The 

 rotation of the earth on its axis causes every place to move east- 

 ward more rapidly than those more distant from the equator ; hence 

 all poleward currents are continually reaching districts moving east- 

 ward less rapidly than themselves, and thus outstrip them, or move 

 by them eastward. The reverse of all this obtains in the case of 

 currents from high to low latitudes ; relatively, to the parts of the 

 earth they successively reach they move westward ; more correctly, 

 less rapidly eastward. In fine, warm currents moving towards the 

 poles impinge on the eastern shores of the oceans to which they 

 Deloug, and cold currents proceeding towards the equator fall on the 

 western shores. Amongst the great currents of the Atlantic the most 

 celebrated is the Gulf Stream, which, from Cape Florida, pursues a 

 north-easterly course, takes the British Isles in its journey, and, 

 according to Scoresby, even reaches Spitzbergen. Britain is bene- 



