172 Mr. J. Croll on the Physical Cause of Ocean-currents. 



sources of heat than those noticed by me; but the omission 

 does not diminish the importance of those to which I have 

 referred. Had I been writing a treatise on meteorology, I 

 should no doubt have referred as well to the influence of 

 aqueous vapour as to many other sources of heat which I have 

 purposely omitted in my paper on Ocean-currents as being 

 foreign to my inquiry. 



Dr. Carpenter objects to my statement that " the greater 

 part of the moisture received at the equator is condensed and 

 falls as rain in those regions," and refers me to the case of the 

 Red Sea, where, although evaporation is excessive, almost no 

 rain falls. But is it not an established fact, that the greater 

 part of the water evaporated in intertropical regions does 

 actually fall as rain in those regions? The reason why the 

 vapour raised from the Red Sea does not fall in that region as 

 rain, is no doubt owing to the fact that this sea is only a nar- 

 row strip of water in a dry and parched land, the air overhead 

 being too greedy of moisture to admit of the vapour being de- 

 posited as rain. But over a wide expanse of ocean, where the 

 air above is kept to a great extent in a constant state of satura- 

 tion, the case is totally different. 



I continue my quotation : — " Until corrected by Mr. Findlay, 

 Mr. Croll assumed that the whole of the true Gulf-stream con- 

 tinues to flow in a N.E. direction ; whereas it is unquestionable 

 that a considerable proportion of it (probably more than one 

 half) turns southwards to the east of the Azores, and reenters 

 the equatorial current " (§ 104). 



I am not aware of having advanced any thing which could 

 lead Dr. Carpenter or any one else to suppose that I was of 

 opinion that the whole of the Gulf-stream flows in a N.E. di- 

 rection, or that I was ignorant of the existence of the S.E. 

 branch. Nor do I remember having seen the correction by Mr. 

 Findlay to which he refers. To suppose that I knew of the 

 existence of the N.E. but not of the S.E. branch, is to assume 

 that I had never seen a chart of the Gulf-stream. If I had 

 seen a chart, how could I possibly have observed the N.E. 

 branch without at the same time perceiving the other ? It 

 would be just as possible to look one's friend in the face and 

 notice his left eye without seeing his right. 



In reference to these four reasons or arguments designed to 

 show that my figures are valueless, there must be some con- 

 fusion of ideas. The point to be proved is, that by some wrong 

 method I have been led to form either an erroneous estimate of 

 the quantity of heat conveyed by the Gulf-stream, or the effects 

 resulting from that heat. This is what Dr. Carpenter proposes 

 to do ; but no sooner does he make this proposal than he com- 



