1872.] c Shearwater 9 Scientific Researches. 601 



" pass freely above the peaks of all but the highest mountains, are able 

 " to pursue an almost unbroken course over tropical and subtropical 

 " latitudes, until they come to those more northern regions where the 

 " act of condensation releases probably three-fourths of their heat"*. — 

 But, says Mr. Croll, " the heat of our south-west winds is derived, not 

 " directly from the Equator, but from the warm water of the Atlantic — 



fC in fact from the Gulf-stream The greater part of the moisture of 



(i the south-west and west winds is derived from the ocean in temperate 

 " regions . . . The greater part of the moisture received at the Equator is 

 " condensed and falls as rain in those regions." Now to any one who 

 examines the proportion borne by the area of the true Gulf-stream, before 

 its easterly bend, to that of the great Sargasso sea of the Mid- Atlantic, 

 which has a temperature only a few degrees lower than that of the Florida 

 Current in corresponding latitudes, and in no way dependent upon it, the 

 assertion that the warmth and moisture of our S.W. winds is essentially 

 dependent on the Gulf-stream, is obviously untenable. So, also, is the 

 statement that moisture cannot be thus conveyed from Intertropical to 

 Temperate regions, because the heated air charged with it must ascend at 

 once into regions so cold that all its moisture will be condensed : for if 

 this were the case, the enormous mass of water raised by evaporation from 

 the surface of the Red Sea (calculated by Dr. Buist as equal to eight feet 

 of depth per annum) ought to fall back again into the Red Sea or the area 

 immediately surrounding it ; and yet, as is well known, the greater part of 

 that area is almost entirely rainless. 



104. Fourthly, until corrected by Mr. Findlay, Mr. Croll assumed 

 that the whole of the true Gulf-stream continues to flow in a N.E. 

 direction ; whereas it is unquestionable that a considerable proportion of 

 it (probably more than one half) turns southward to the east of the 

 Azores, and re-enters the Equatorial current. This portion, however, 

 Mr. Croll regards as the principal heater of the S.W. winds which im- 

 part warmth to the British Islands ; whilst the portion of the current 

 which he assumes to flow past our Islands up into the Arctic seas, he re- 

 gards as the heater of the S.W. winds which go to warm Norway 

 and the North of Europe. — Now the fact is, as I shall show hereafter 

 (§ 147), that the large division of the Gulf-stream which thus turns 

 southwards possesses no excess of temperature above the general mass of 

 Atlantic water in that region, being only recognizable by its movement. 

 And as to the portion which passes northwards, we shall see that its Area 

 is so small in relation to the general surface of the Atlantic through 

 which it passes, and that its Temperature is so little in excess of that of the 

 water on either side of it, as to render its Thermal effect very insignifi- 

 cant (§§ 150, 157). 



105. The difference between Mr. Croll's representation of the amount 

 of Heat actually carried out by the Gulf-stream, and the actual facts of 



* ' Principles of Geology,' Eleventh Edition, vol. i. p. 238. 



2x2 



