96 Mr. J. Croll on Ocean- currents in relation to 



in the form of heat carried by warm currents from the equator 

 to the temperate and polar regions, and also the quantity of ne- 

 gative energy (cold) carried by cold currents from the polar re- 

 gions to the equator, we shall find that they are sufficient to re- 

 duce the difference of temperature between the poles and the 

 equator from 218° to 80°. 



The quantity of heat received in the latitude of London, for 

 example, to that received at the equator is about as 12 to 8. 

 This, according to theory, should produce a difference of about 

 125°. The temperature of the equator above that of space, as 

 we have seen, would be 374°. Therefore 249° above that of 

 space would represent the temperature of the latitude of London. 

 This would give 10° as its temperature. The stoppage of all 

 ocean and aerial currents would thus increase the difference be- 

 tween the equator and the latitude of London by about 85°. 

 The stoppage of ocean-currents would not be nearly so much 

 felt, of course, in the latitude of London as at the equator and 

 the poles, because, as has been already noticed, in all latitudes 

 midway between the equator and the poles the two sets of cur- 

 rents to a considerable extent compensate each other ; viz. the 

 warm currents from the equator raise the temperate, while the 

 cold ones from the poles lower it; but as the warm currents 

 chiefly keep on the surface and the cold return-currents are prin- 

 cipally undercurrents, the heating effect very greatly exceeds 

 the cooling effect. Now, as we have seen, the stoppage of all 

 currents would raise the temperature of the equator 55°; that 

 is to say, the rise at the equator alone would increase the differ- 

 ence of temperature between the equator and that of London by 

 55°. But the actual difference, as we have seen, ought to be 

 85°; consequently the temperature of London would be lowered 

 30° by the stoppage of the currents. For if we raise the tem- 

 perature of the equator 55° and lower the temperature of Lon- 

 don 30°, we then increase the difference by 85°. The normal 

 temperature of the latitude of London being 40°, the stoppage of 

 all ocean and aerial currents would thus reduce it to 10°. But 

 the Gulf-stream raises the actual mean temperature of London 10° 

 above the normal. Consequently 30° + 10° = 40° represents the 

 actual rise at London due to the influence of the Gulf-stream 

 over and above all the lowering effects resulting from arctic 

 currents. On some parts of the American shores on the lati- 

 tude of London, the temperature is 10° below the normal. The 

 stoppage of all ocean- and aerial currents w r ould therefore lower 

 the temperature there only 20°. 



It is at the equator and the poles that the great system of 

 ocean and aerial currents produces its maximum effects. The 

 influence becomes less and less as we recede from those places, 



