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



perature of the Atlantic would not actually remain 30° lower than 

 at present; for heat would flow in from all sides and partly 

 make up for the loss of the stream. But nevertheless 30° re- 

 presents the amount of temperature maintained by means of the 

 heat from the stream. And this, be it observed, is taking the 

 volume of the stream at a lower estimate than even Mr. Findlay 

 would be willing to admit. Mr. Findlay says that, by the time 

 the Gulf-stream reaches the shores of England, it is supposed to 

 cover a space of 1,500,000 square miles. " The proportion of 

 water that passes through the Straits of Florida will not make/' 

 says Mr. Findlay, " a layer of water more than 6 inches thick 

 per diem over such a space." But a layer of water 6 inches 

 thick cooling 25° will give out 579,000 foot-pounds of heat per 

 square foot. If, therefore, the Gulf-stream, as Mr. Findlay as- 

 serts, supplies 6 inches per day to that area, then every square 

 foot of the area gives off per day 579,000 foot-pounds of heat. 

 The amount of heat received from the sun per square foot in 

 latitude 55°, which is not much above the mean latitude of 

 Great Britain, is 1,047,730 foot-pounds per day, taking, of 

 course, the mean of the whole year ; consequently this layer of 

 water gives out an amount of heat equal to more than one half of 

 all that is received from the sun. But assuming that the stream 

 should leave the half of its heat on the American shores and 

 carry to the shores of Britain only 12J° of heat, still we should 

 have 289,500 foot-pounds per square foot, which notwithstand- 

 ing is more than equal to one fourth of that received from the sun. 

 If an amount of heat so enormous cannot affect climate, then 

 what can possibly do it ? 



I shall just allude to one other erroneous notion which pre- 

 vails in regard to the Gulf-stream ; but it is an error which I 

 by no means attribute to either Mr. Findlay or to Dr. Carpen- 

 ter. The error to which I refer is that of supposing that when 

 the Gulf-stream widens out to hundreds of miles, as it does 

 before it reaches our shores, its depth must on this account be 

 much less than when it issues from the Gulf of Mexico. Although 

 the stream may be hundreds of miles in breadth, there is no ne- 

 cessity why it should be only 6 inches, or 6 feet, or 60 feet, or 

 even 600 feet in depth. It may just as likely be 6000 feet deep 

 as 6 inches. 



The reason why such diversity of opinion prevails in regard to 

 Ocean-currents. 



In conclusion I venture to remark that more than nine tenths 

 of all the error and uncertainty which prevail, both in regard to 

 the cause of ocean- currents and to their influence on climate, is 

 due, not, as is generally supposed, to the intrinsic difficulties of the 



