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



of the Gibraltar current is little more than 1 foot-pound per 

 pound of water, an amount of energy totally inadequate to pro- 

 duce the current. 



The Baltic Current. 



The entrance to the Baltic Sea is in some places not over 50 

 or 60 feet deep. It follows, therefore, from what has already 

 been proved in regard to the Gibraltar current, that the influ- 

 ence of gravity must be even still less in causing a current in 

 the Baltic strait than in the Gibraltar strait. 



Dr. Carpenter's Objections to my Estimate of the absolute amount 

 of Heat conveyed by the Gulf -stream. 



After giving a full exposition of his theory, he closes with the 

 following remarks : — 



" Having thus fortified my own position by showing that the 

 power I have invoked has a real existence and a most extended 

 and varied operation instead of being a figment of my own 

 imagination (as Mr. Croll represents it), I shall venture to 

 attack the stronghold of my adversaries by showing that the 

 Gulf-stream at the point of its greatest ' glory ' can by no means 

 claim the heating-power which they assign to it" (§ 39). He 

 then proceeds to criticise the data on which my estimate was 

 formed. But surely in my paper on the subject I must not 

 have expressed myself with sufficient clearness, seeing that Dr. 

 Carpenter has on several important points misunderstood me. 



He begins with the following quotation from my paper in the 

 Philosophical Magazine, February 1870, p. 82. "From an ex- 

 amination of the published sections some years ago," says Mr. 

 Croll, " I came to the conclusion that the total quantity of 

 water conveyed by the stream is probably equal to that of a 

 stream fifty miles broad and 1000 feet deep, flowing at the rate 

 of four miles an hour"*. He then assumes that all my con- 

 clusions regarding the enormous amount of heat conveyed by 

 the stream, and from which my inferences as to his theory were 

 drawn, were based upon this estimate of the volume of the stream. 

 This, it is true, was the volume adopted in my former estimate 



* The above gives 5,575,680,000,000 cubic feet per hour as the volume 

 of the stream. Professor Wyville Thomson, in reference to this, says, " I 

 see no reason whatever to believe this calculation to be excessive" ( ( Nature' 

 for July 27, 1871, p. 252). Dr. Colding, in his recent elaborate memoir 

 " On the Gulf-stream," estimates the volume at 5,760,000,000,000 cubic 

 feet per hour. Maury, as we have seen, estimates it at 6,165,700,000,000 

 cubic feet, and Herschel at 7>359,900,000,000 cubic feet. But in my paper 

 the calculations were made on the assumption that the volume is only 

 2,787,840,000,000 cubic feet. 



